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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  • mm2587 - Monday, November 08, 2010 - link

    You guys honestly didn't include the 460 ftw in the charts after the whole mess with the launch article, or at least mention it in passing in your conclusion? Sure I can go back and compare the results with the past articles but that not the point. Here's your chance to compare overclocked cards to overclocked cards and you don't even mention it.

    This article really must be a joke after all it ends with an overclocked "kicking" a reference 460 to the "curb"
    Reply
  • keitaro - Monday, November 08, 2010 - link

    If it's not mentioned, then it is not mentioned. You said it yourself that you can just grab the numbers from the launch article. So why complain about it? If you believe that this is an omission or something missed, why can't you just point it out instead of making a fuss about it? Reply
  • whatthehey - Tuesday, November 09, 2010 - link

    (I'm posting here because otherwise you get lost in the fanboy "debate" below.... My response isn't really to either of the above two readers.)

    You know, I didn't get into the initial 6850 + 460 FTW brouhaha because I figured any sensible being wouldn't have a problem with it. I also didn't bother wading through any of the comments on the "what do you want" follow up. I thought the amount of noise a select few made was stupid then, and it's even dumber now!

    AnandTech, you first need to wade through the users posting comments and do some research on past "input". Half of the users complaining and calling your credibility into question have no credibility to begin with! I swear there were a ton of new users that we have never heard from before. Seriously, do a Google on the most vocal user names and this site. Here are the nay-sayers posting on this article's comments; most of the others (i.e. 7Enigma in particular) are mostly interested in the bottom line rather than fanboy rage. So, here's a Google of site:www.anandtech.com {username}.

    AnandThenMan: almost never a nice thing to say, and definitely anti-Nvidia. Vote: AMD fanboy
    vedye: Never posted before GTX 460 and anti-Nvidia. Vote: AMD fanboy
    spigzone: Off and on poster over time, but EXTREMELY vocal on the 460 FTW issues. Definitely a squeaky wheel, but only represents ONE person.
    Ramon Zarat: Past posting history indicate strong AMD/ATI preference. Vote: AMD fanboy

    If you were to wade through the mass of posts on the two 6800 articles and eliminate flame wars, trolling, etc. you probably only get about 10% of the posts, and they're still a minority.

    I'd say the vase majority of us simply want more data. Had you overclocked a 6850 in the initial review, there would have been nothing to stand on. Maybe a simple statement of, "Time constraints (and lack of a retail card) led us to running stock settings; we'll be back next week with more data on 6850 overclocking." What's really stupid is that the conclusion wasn't even in favor of the GTX 460. All it said was, "yes, an overclocked 460 can do quite well, but it draws more power and costs more so it's not really desirable."

    This is making mountains out of mole hills and then some. Move along, nothing to see here people. AMD and NVIDIA both compete fairly well. AMD has a better midrange part right now, but NVIDIA has faster parts if you're willing to pay the price and power. Two years ago it was all NVIDIA, and back in the 9800 days it was all ATI.
    Reply
  • Galid - Tuesday, November 09, 2010 - link

    I still love the fanboys debating for some more performance there and a little less there. Trading blows for some more peanuts on a side and you trow in a 5-10$ difference then light they'll bring wood and burn someone on a stake.

    And when there's not enough difference to speak of then they throw in driver issues and such not so credible arguments. Or how they toasted every card they bought from the other competitor which is actually run by a subsidiary of the devil himself.

    Always making my day when I see a new article about video card I jump right to the bottom and read the comments! :D
    Reply
  • GeorgeH - Monday, November 08, 2010 - link

    HULK SMASH!! LOUD NOISES!! FANBOY RAAAAAAAAAAAAAAGE!! ;)

    More seriously, an OC 460 is a little faster than a stock 6870. An OC 6850 is (very surprisingly) almost the same. At $180 for a 6850 vs $190 for a 460 1GB (current Newegg prices), the 6850 wins - although with such a tiny price and performance differential means it really boils down to color preference: do you like red or green? Competition FTW.

    "Kicking to the curb" is over the top, but if it keeps the I❤AMD crowd from throwing another tantrum I'm cool with it.
    Reply
  • CeriseCogburn - Thursday, August 23, 2012 - link

    Oh, 6850 compute performance fail. Now it matters say the amd fans - so hope they didn't do the stupid and get the 6850. Reply
  • Ryan Smith - Monday, November 08, 2010 - link

    It was made abundantly clear to us in the comments in our follow-up piece and in emails to us that you guys disapproved of our inclusion of non-reference cards in articles. As we strive to reflect the needs and wants of you, our reader, we have taken your advice to heart. You will not be seeing the FTW or similar cards in any articles besides their associated roundups. As such articles like this will focus solely on the series being reviewed, and will not contain results from overclocked or otherwise non-reference cards that are not among the cards being reviewed. Reply
  • mac2j - Monday, November 08, 2010 - link

    It was more about comparing: Reference vs Reference, OC vs OC

    Though I agree the best place for the 460 FTW is in a 6970 OC comparison article not a 6950 one.

    As for this article "MSI R6850 OC is just all-around worse" makes no sense to me - as someone who doesn't care about noise and doesn't know a single person that really does in that kind of range ... of all these cards I would buy the MSI as it has by far the best price to performance.

    I mean it's the only card that outperforms the 5850 and even, in a couple cases, the 6970 ... that's more performance for ~$50 less with similar noise... so calling it "all-around worse" is just crazy talk.... crazy talk man
    Reply
  • Targon - Monday, November 08, 2010 - link

    You mean 6870, right? The 6950 and 6970 have yet to be reviewed, at least in public, and we don't have any release date for the new high end parts, which will finally allow the 5870 to fade away as the top single-GPU cards from AMD. Reply
  • mac2j - Monday, November 08, 2010 - link

    Ugh yea 68XX not 69XX ... been reading too many Cayman preview articles - sorry. Reply

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