We wanted to see if these new AMD models have more overclocking headroom than their predecessors, so we performed some quick and dirty overclocking tests.
In the case of the Phenom II X2 560 and Phenom II X4 970 Black Edition CPUs, we simply raised the voltage to 1.475 V, along with the CPU multiplier, until we figured out the limit of Prime95 stability. The Phenom II X6 1075T is a little trickier since it is not a Black Edition processor and its CPU multiplier is locked. In this case, we increased the voltage to 1.475 V and the reference clock speed until we achieved the highest stable setting (each processor's overclocking details are reported below).
The Phenom II X2 560 makes it to 4 GHz, which is just about exactly what we got out of our Phenom II X2 555 at the beginning of the year. However, our attempt to unlock dormant CPU cores (in order to turn the X2 into an X3 or X4) was met with failure. We were actually a little surprised, because this is the first Black Edition Phenom II X2 that we haven’t been able to successfully unlock. The 700 MHz overclock helps performance, regardless.
Our experience with the Phenom II X4 970 is slightly different. Our first sample was able to hit 3.9 GHz through multiplier-based overclocking, which is about what we expect to achieve with a Phenom II X4 965. However, we also have a Phenom II X4 970 on hand that benefits from an AMD process improvement.
The newer revision can be identified with the letters “AACDC” on the lid, as opposed to the previous sample that read “AACAC.” AMD's representative assures us that the newer revision is the only one that will make it to retail channels. Both CPUs are revision RB-C3 and Stepping 3, according to CPU-Z, but the new version does achieve a higher overclock of 4.1 GHz. Prime95 stress tests run fine, but SiSoft Sandra arithmetic benchmarks crash and we had to raise the voltage to 1.55 V in the BIOS to achieve stability. This is a little higher than the 1.5 V maximum we usually use, but the temperatures remained quite low, so we allowed ourselves to indulge a bit.
The multiplier-locked Phenom II X6 1075T managed to make it to 3.75 GHz at 1.475 V with a bus increase to 250 MHz. This overclock really revitalizes this CPU, as you can see in the benchmarks.
We also include the overclocked Core i5-750 results from our last System Builder Marathon:
In the SiSoft arithmetic CPU benchmark, the overclocked Phenom II X4 and X6 show large improvements over the stock speed, but the dual-core Phenom II doesn’t demonstrate much of an advantage when pushed. The Core i5-750 shows a huge boost in the Dhrystone results, but the Whetstone numbers fall short of the overclocked Phenom II X4 970 and the stock Phenom II X6 1075T.
We choose TMPGEnc for our application benchmark because it has two different encoding algorithms that take advantage of varying processor strengths. While the DivX codec demonstrates a huge performance increase with the Phenom II X6’s hexa-core architecture, the Xvid codec prefers raw speed and Intel’s design.
With StarCraft 2 as our game benchmark, you can see the overclocked Phenom II X6 1075T surpasses even the 4.1 GHz Phenom II X4 970 by a small margin. The overclocked Core i5-750 really shines here, though, sailing by all of the other processors.