Ultra Spec Performance
We found the Ultra Spec quality preset to be extremely demanding when testing The Witcher 2. In fact, there is no single graphics card that will provide playable performance at resolutions above 1680x1050. At that resolution, the dual-GPU GeForce GTX 590 and Radeon HD 6990 flop delivering a flimsy 36fps and 21fps.
Interestingly, the HD 6990 was slower than the single-GPU GTX 580 when using the Ultra Spec quality preset. Although the 11.5a hotfix provides Crossfire support, we found that it was not working properly when using the Ultra Spec settings. As a result, we do not believe there is an AMD configuration that can handle UberSampling.