Benchmarks: Overclocking PerformanceWe had already anticipated the Radeon HD 4890 would be a great overclocker from numerous early reports online. Our final stable overclock of 970MHz for the core and 1165MHz for the memory is impressive enough, just slightly shy of the 1GHz core clock speed.
The GeForce GTX 275 did not fair too bad either with an extra 109MHz squeezed out of the core (741MHz) and a final 1278MHz for the memory.
Both the Radeon and GeForce cards were overclocked using the stock coolers which in these Asus products abide by the reference models from each GPU manufacturer. Using an aftermarket cooler will likely bring some extra OC headroom but perhaps more importantly, improved temperature levels and less noise (see next page for more).
More detail on how these overclocks affected actual performance output is below.
Both graphics cards received an 18% performance boost at 2560x1600 in UT3 thanks to the overclock. The Radeon HD 4890 rendered an additional 7fps, while the GeForce GTX 275 managed to produce 8fps more.
Unfortunately for the Radeon HD 4890 the extra 18% performance made it just 1fps faster than the stock GeForce GTX 275. The GeForce GTX 275 overclock on the other hand allowed it to match the performance of the GeForce GTX 285 and Radeon HD 4870 X2 graphics cards.
The Radeon HD 4890 didn't see much of a gain in Left 4 Dead when overclocked. The result at 2560x1600 was just an 8% increase, and perhaps this explains why the Radeon HD 4890 does not fair very well in this game to begin with. The Radeon HD 4890 was barely faster than the Radeon HD 4870 in Left 4 Dead and overclocking it further didn't help greatly.
The GeForce GTX 275 received a 17% performance boost at 2560x1600 which again allowed it to overcome the GeForce GTX 285 and perform on par with the Radeon HD 4870 X2. Given that the core clock speed of the GeForce GTX 275 has been boosted by ~17%, and the memory frequency has been increased by 13%, we are seeing maximum returns from this graphics card.