Unfortunately at this point we were only able to overclock the Radeon HD 5870 using the Catalyst control panel, which allows for a maximum core clock of 900MHz, while the memory can only be pushed as high as 1300MHz. Despite the high operating temperatures when using the default clock frequencies, the Radeon HD 5870 was perfectly stable at 900MHz.
Our small overclock meant that the Radeon HD 5870 could deliver 8% more performance in Unreal Tournament 3 at 2560x1600, with frame rates going from 60 to 65fps. This is a decent performance boost at such an extreme resolution, and even 5fps extra will be noticed here.
When testing with Left 4 Dead at 2560x1600, we also see a performance gain of 5fps, which allowed the Radeon HD 5870 to pull ahead of the Radeon HD 4870 X2. Overall we have seen some nice results at extreme resolutions, and we hope to try and overclock this graphics card further very soon.