CrossFire And SLI: Battlefield 3 And Crysis 2
Hold onto your collective rear-ends. A second Radeon HD 7950 adds 96% to the single-card result without anti-aliasing and 98% when you apply 4x MSAA, making Battlefield 3 more than playable at 2560x1600 with Ultra quality settings.
Knowing what we know about the 7950’s weakness in Crysis 2 under DirectX 9, you’re going to want to stick with DirectX 11. A second Radeon HD 7950 increases performance by 92%. That’s enough of a speed-up to wiggle past a pair of GeForce GTX 580s and absolutely destroy the four processors wielded by two Radeon HD 6990s.
We couldn’t come up with any good reason to explain the quad-GPU failure under DirectX 11, but a far better DirectX 9 result makes it pretty clear that the problem is related to API choice.