Overclocking: Performance, Power, Temperature, & Noise

Half of our results focus on our 6850s at their stock clocks, but the other half of our results focus on the card when it comes to overclocking. As a lower clocked Barts card, 6850 cards not binned for poor maximum clocks should have a fair bit of overclocking room as AMD intended for the design to hit 900MHz+. The 6850’s power efficiency pretty much has to go out the window here, but in return we can capture some significant performance gains.

Overclocking Results
  Stock Clock Max Overclock Stock Voltage Max Overclocked Voltage
Radeon HD 6850 Reference 775MHz 940MHz 1.094v 1.172v
XFX Radeon HD 6850 775MHz 940MHz 1.148v 1.172v
MSI R6850 OC 820MHz 960MHz 1.148v 1.22v
Asus EAH6850 790MHz 960MHz 1.148v 1.22v

When overclocking, we found 3 things:

  1. All of the cards could hit 850MHz core at stock voltage
  2. All of the cards could hit 940MHz core at 1.172v, the 6870 load voltage
  3. We had to give the cards significantly more voltage to get above 940MHz. This culminated at 1.22v on the Asus and MSI cards for 960MHz

Based on these results we went ahead and benchmarked the Asus card at 850/1150, 940/1150, and 960/1150 to showcase the performance at these overclocks, while capturing data for all of the cards at 1.172v, and the Asus and MSI cards at 1.22v.

While it’s possible to hit 960MHz with enough voltage, in practice it’s not worth the effort. The Asus and MSI cards jumped in power consumption, temperature, and noise by around 20W, 3C, and 2dB each, for a performance difference of under 2%.  On a higher-end card where performance is the only attribute that matters this wouldn’t really matter, but we would not consider this a useful tradeoff on a petite card like the 6850.

As for memory overclocking, we hit at solid wall at 1150MHz as none of our cards could do 1200MHz without artifacting. However 1150MHz didn’t trigger performance degradation due to error correction-induced retransmission, so it looks to be a safe frequency for all cards. The limit we believe lies solely with the memory controller, which was a conscientious decision by AMD to trade memory clocks for a smaller die. As a result the controller reaches its limit before we can even push the 5GHz GDDR5 to spec.

Something that caught us completely off-guard in our results is just how well the overclocked 6850 did. Even at the “mere” speed of 850/1150, it’s faster than the 6870 in 3 out of our 5 games; and the 6870 still has a core clockspeed advantage and more SIMDs! The advantage for our overclocked 6850s is that the memory clock of 1150MHz (4.6GHz effective) is faster than the 6870’s memory clock of 1050Mhz (4.2GHz effective), and this looks to be the reason for the difference. Based on all the data we have, Barts looks to be memory bandwidth starved in around half the games we use. From this it looks like a good memory overclock is going to go a long way on the 6850 and 6870 towards improving performance.

As for how much of an overclock is necessary, this depends on the game. When Barts is memory bandwidth starved, the 940Mhz and 960Mhz memory overclocks provide only a small boost; while on shader-bound games like Crysis there’s a very tangible benefit. Combine the memory overclock with a 940Mhz core overclock and the 6850 can meet or beat the 6870 every single time. The voltage increase necessary to achieve this core overclock comes at a price however.

Starting with power consumption, the voltage increase necessary for 940MHz is around 20W-30W under FurMark for our reference and near-reference clocked cards, and less for the MSI card since it already has a notable factory overclock. If nothing else, 1.172v gives up all the power advantages over the Radeon 5850, though as we’ve seen it pays off with a very notable performance advantage over the 5850.

For the partner cards in today’s roundup, the temperature runup from overvolting isn’t too bad, with the worst card only hitting 81C under FurMark and becoming progressively cooler from there. However the reference 6850 is an entirely different story: it hits 93C under FurMark, which is hotter than what we’re comfortable with for Barts, particularly since it’s brand new. If reference-style cards show up on the market, we would not recommend overvolting them, at least not to 1.172v. Meanwhile the XFX card with its focus on temperature tops this chart, still only hitting 74C under FurMark. The cooling on this card is so good that we suspect the VRMs will burn up long before the GPU will when overvolting.

Finally we come to noise. We suspect many buyers will be alright with the power and temperature increases so long as noise remains manageable, so what we have is a mixed bag. Throwing out the reference 6850, we’re left with the XFX card at over 60dB, and while XFX’s focus on temperatures is commendable, it ends up being shortsighted by making the card exceptionally loud here. This is followed by the double-overclocked MSI card, which at 58.7dB is over 3dB louder than the 6870, but is only encroaching on the 5870. It’s too much noise for the performance, but compared to first-gen 40nm cards it’s not the end of the world.

This leaves us with the Asus card. While it does jump by 6dB due to our overclocking, it had such a massive lead at stock that this only makes it about as loud as the GTX 260 and Radeon HD 4870. The idea of a near-silent card has gone out the window at this point, but we would consider it a very manageable level of noise for the performance offed with the 940/1150 overclock. Certainly it’s the most balanced of the cards, as it sacrifices only little in the way of cooling (78C in FurMark) for the lower level of noise generated.

Power, Temperature, & Noise Final Thoughts
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  • Etern205 - Monday, November 8, 2010 - link

    XFX cost $10 bucks more and has the exact same spec as the reference.
    Where does that $10 go to? To that "XFX" cut out on the I/O plate?

    All of them went and have gone with a single standard display port, rather than the 2x mini DP, thus you can only have 3 monitors rather than 6 in Eyefinity mode.
    Reply
  • Etern205 - Monday, November 8, 2010 - link

    Disregard the 2nd complaint, looks like the HD6850 do not have 2x mini DP, except for the reference card in the press shots Reply
  • tigersty1e - Monday, November 8, 2010 - link

    I think everybody was mad about the other article because it was pinning a stock ATI card with an OC'd Nvidia card.

    When you bring in an article about OC'd ATI cards, I want to see the competition's OC'd cards.
    Reply
  • totenkopf - Monday, November 8, 2010 - link

    I only now checked the prices...

    Is this a joke? What is all the fuss about the GTX460 FTW? It's the same price as a stock 5850 or 6870 and ~same performance. If you were a rational human wouldn't you buy either of those AMD cards and just OC them to the gills like the FTW... but smoke the crap out of it? more importantly, why are people up in arms about including it in this review when it isn't even supposed to compete with the 6850? It's a bad buy any way you slice it it seems.
    Reply
  • Quidam67 - Tuesday, November 9, 2010 - link

    This drama about the GTX460, in relation to *this* article is out of hand.

    Frist off, the evga 460 FTW card is a Factory overclock, but this article is about the custom overclocking potential of the HD6850 cards.

    So if they were going to include GTX460 cards, it is irrelevent what the stock clock is. What is relevent is, after being custom overclocked, which card comes out first?

    Along those lines, most people already acknowledge that this sort of comparrison is best saved for the HD6870 cards where overclocked GTX460's are more likely to meet their match.

    Although I did not agree with AT's choice to include the evga GTX460 FTW in the HD 6850/70 launch article, I fail to see how they have done anything wrong with this piece. Perhaps you just need to wait for the right article to come out -so here's a suggestion, why don't you just ask for it, without hurling insults?

    Lastly, I think this forum (sadly) needs moderation. Some of the behaviour here is not of an acceptable standard, and dilutes the many quality posts that are made by people of a more rational and civil nature.
    Reply
  • vedye - Tuesday, November 9, 2010 - link

    It's called credibility crisis. I just have a different feel to the Anandtech website now. Reply
  • Andyburgos - Tuesday, November 9, 2010 - link

    (Takes a long breath, and warns about a long post)

    Hello everyone, and specially to the AnandTech staff.

    This is my first post, for I have created an account specially for this "overclocked cards or not?" affaire; I´m late to the party, and that´s because my opinion is maybe very different to what I have seen until now, and I wouldn´t like to upset anyone.

    I´m 21 years old, I work with computer hardware since I was 14, and not even living on the other side of the world (Argentina) has changed the fact that AnandTech is and was so important for my computer life as my first Athlon XP, my first 64-bit OS install or my first dual core processor. AT and the now derailed Tom´s Hardware were, back in the early 2000s, my main source of information, and the great articles on those pages helped me understand many things about computer hardware and software. Anand is GIFTED at explaining things, and I have yet to find one of his articles being boring; and the new reviewers, a bit unpolished at first and way improved now, are doing great and they provide new points of view: they make AT a more complete site.

    The fact that I live in Argentina and yet AT is my primary site for hardware information is a testament to the fact that I find them completely unbiased and absolutely professional in their reviews. In my country, while there are a couple of good publications about computer science, we are very far from this great standards.

    However, and with the most absolute respect, I think you need to review some of your reviewing standards. The staff has grown, and along the new points of view have come very different article layouts, wich make them a bit "harder" to read; the video card market has changed a lot in the last five or so generations, and you need to think about what to do with factory overclocked cards, as this case; processors have also changed a lot, and even Turbo results are worth discussing (i.e., what role plays thermal throthling in Intel and AMD processors and how does that affect performance instead of providing absolute numbers). As a loyal reader, wich has read every single hardware article from 2003 to now, I feel entitled to tell you what I think is best in this case, and as a general guideline to provide standars in other reviews:

    1) AVAILABILITY OF THE PRODUCT: in the GTX 460 FTW case, I think you missed that a bit. I mean, it may be available in USA, but in Argentina, while we keep up the pace in the generation of the cards, we do not in brand availability. The FTW is hard to find here, I think it must be in other "remote" locations, and a part of your readers are from there; at least in my city, you´re being read more frecuently than most national publications.
    Of course this does not affect the benchmarks, but it deserves a disclaimar as much as the inclussion of the FTW.

    2) PARTICULARITY (couldn´t find a better word in my dictionary) OF THE PRODUCT: the FTW was a heavily overclocked, non reference, not-so-broadly-available card; it can not be compared in any way to a reference Radeon 68x0. However, it CAN and it MUST be compared DIRECTLY with overclocked, non reference, not-so-broadly-available card as the MSI 6850. The GTX470 might be very competitive in terms of performance with the 6870, but if you say "ok, the 470 is faster, but mind you, it is a hot and power hungry card" and leave it at that you are openly aproving a very, lets be polite and say "unpolished" mArch as the GF100 is, and by oblitterating the fact that the GTX470 is basically lowering the price for making up all the mess they made in the first place you are making the same ripoff that nVidia made by renaiming the 8800GT 9800 GT and then GTS250, or AMD by calling Barts 68x0. The same goes for Intel: their naming scheme SUCKS BADLY, and you should be complaining about the fact that some i5 series are even dual core, or even worse i7s in notebooks. I´m saying this because I sincerely believe that Anand is one of the smartest thinkers in the I.T. industry, and he has to be heard.

    3) REFERENCE OR NOT: I will put it as simply as I can. Comparing a GTX460 FTW with a Radeon GeForce 6850 is like comparing a 1992 Nissan 240ZX stripped of all the inner panels, seats, air conditioning, etc., and the engine tuned to the max with a 2009 370Z. Both of thouse cars have made tradeoffs (noise for speed, size for performance for example) and both run at a similar final speed, but they do so in a different way. I think it is not a fair comparison: with the FTW, you get warranty along a heavy overclock, so the above comparison is not very fair, but the idea remains: compare by price, and reference or not. For example, you say that the FTW is worth having a different name such as GTX461, 465, whatever; but by comparing it to the stock 6850 you are saying "what the hell, it works out anyway" you are doing the same thing that EVGA and nVidia did by calling it 460 FTW.

    4) AT always changes for the best, you are very smart at changing for this is a constantly moving industry. Review your standards permanently, and listen to your readers but don´t get mad at it: can´t please everyone.

    Sorry for the long posts, and for those that will inevitably think I am a fanboy I will tell them that my 4 last video cards were Radeon 9600SE, GeForce PCX5900, GF 7300 GT, and recently GF9600GT.

    Best regards Anand & staff, and keep building the best hardware site on the net.
    Reply
  • vshin - Friday, November 12, 2010 - link

    Ryan, dunno if you're still reading these comments but I just want to thank you for a good review of the various 6850 cards. It was a tremendous help. Reply
  • Oxford Guy - Friday, November 12, 2010 - link

    Is there a way to change the fan speed profile so it won't be so aggressive/loud?

    Since it's using a vapor chamber, one would assume it should be able to run with a slower fan speed.
    Reply
  • King.Koba - Thursday, December 2, 2010 - link

    Now that Sapphire's 6850 Toxic edition is out. I'd like to see it compared to these other factory over-clocked cards. Sapphire has been the biggest player in ATI/AMD cards for a long time and their Toxic series has always brought a little more to the table.

    This time, it has a 6870 style PCB with 2 6pin connectors. The potential of having 75 more watts available might allow it to push far past the other cards which were tested. It would be interesting to see if that potential translates in real world testing.
    Reply

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