Intel’s Core i5-655K & Core i7-875K: Overclocked and Analyzed
by Rajinder Gill on May 28, 2010 5:00 AM ESTi5-655K Meets a Cold Snap
Our dual rotary cascade is capable of holding -108 Celsius temperatures under full load from a Clarkdale processor clocked to 5.9GHz. For the i5-655K we’re kicking-off with Vantage:
Almost 200MHz behind the i5-661 in this test and around 100MHz behind our retail i5-540. Luckily for the i5-655K, this particular benchmark is not high on most peoples' agenda for Clarkdales. The real fun zone is Super Pi 32M:
Again, this comes in behind the i5-661, by around 250MHz this time. There’s nothing additional that the i5-655K offers over our 661 by virtue of its unlocked multipliers – at least up to this temperature. We tried various methods to squeeze more frequency and more performance out of the i5-655K, but were unable to find a better operating point than what we’ve shown here. QPI frequency is limited to around 4.8GHz on this sample, so the only way to really get the best from the chip is to keep QPI close to this level and provide a reasonable amount of memory access latency around the DDR3-2000 mark.
There is a bit of a reprieve for the i5-655K against the i5-540 however, because although the i5-540 manages 6GHz in this benchmark it scores poorly due to a maximum 23x multiplier needing a high BCLK frequency and thus a low QPI ratio to achieve this speed. As such, based upon everything we've seen here, our conclusion is that the performance of this particular i5-655K very much fits its price. There’s certainly enough on-tap to edge out the lesser i3 series in key areas, but we've not seen enough to believe they'll knock the better i5-660+ samples off the podium.
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Rajinder Gill - Saturday, May 29, 2010 - link
Hi,I ran out of time to test any further unfortunately. The emphasis was kept on air/water cooling because it's practical to run 24/7.
Regards
Raja
TheBLK - Saturday, May 29, 2010 - link
I'll ask again. Unless the screen shots are wrong you used BLK clock to over-clock rather than multiplier on the chip.Other reviews kept the BLK at the same value and just used the multiplier and seemed to get higher results.
Rajinder Gill - Saturday, May 29, 2010 - link
Yes I did on the 655-K stock VID (added 2 BCLK because the next multiplier up was too far (133 multiples in frequency is a large jump) :http://www.anandtech.com/show/3742/intels-core-i56...
Also describe why BCLK overclocking is not the way to go on the 655K for performance:
http://www.anandtech.com/show/3742/intels-core-i56...
Finally the 855K - this chip is limited to 4GHz even on water cooling. BCLK overclocking is not going to change that. 167 BCLK at DDR3 1670 is nowhere near stressful for the Lynnfield IMC. Multiplier overclocking is NOT going to make any difference to the clock speed limitation.
-Raja
Rajinder Gill - Saturday, May 29, 2010 - link
Just for you :)http://img7.imageshack.us/f/linpackfailj.jpg/
That is all the water loop can handle (the chip is drawing over 190W). I can drop the multiplier down to 30 (but then we are back to 4GHz).
Hope this helps!
Regards
Raja
DJMiggy - Thursday, June 3, 2010 - link
It seems like you guys used the wrong motherboard or got a dud i7. Other reviewers don't seem to be having as tough a time overclocking these higher.Rajinder Gill - Friday, June 4, 2010 - link
The motherboard is EVGA's E659 - works fine with my i7 870 ES taking it to 4.4GHz Linpack stable. It's the CPU that is the limiting factor here. Bear in mind that not all articles you've read will have stability checked stability with Linpack as well.Later
Raja
DJMiggy - Friday, June 4, 2010 - link
That makes sense. Cool thanks! I appreciate the explanation.ReaM - Saturday, June 5, 2010 - link
I must say, what a crappy K-series! I can bring every i7 860 up to 4ghz. I have tested many of them, so there is really no reason to put any hope into these Ks. Just buy a regular one.My personal sample of 860 runs @ 4200 with 1.29V on air Noctua U12 with low temps.
ReaM - Saturday, June 5, 2010 - link
Did you put Load Line Calibration into LVL2?I don't know what's that called on EVGA. Enhanced Power Slope. VDrop Adjustment. Lynnfield, unlike Bloomfield, likes their load line to be adjusted.
Rajinder Gill - Sunday, June 6, 2010 - link
Makes no difference to the stability of this chip.