Benchmarks: Crysis Warhead, Crysis 2
Instead of using the Crysis Warhead benchmark, we recorded frame rates over 60 seconds of actual gameplay using Fraps. We used action from the level "All The Fury" at the enthusiast quality setting with AA and AF disabled.
When using a single 30 monitor at 2560x1600 we found that the Radeon HD 6990 was 11% faster than the GeForce GTX 590. As we increase the resolution to 5040x1050 that margin is reduced to just 2% in favor of the Radeon HD 6990. Then at 5760x1200 and 7680x1600 the frame rates drop a bit too much, the cards are evenly matched though you won't be playing at these resolutions.
We used Fraps to measure frame rates during a minute of gameplay from the first single-player level called Second Chance for all our benchmarks. The scene is quite busy and should provide a fair representation of the performance you can expect to see on Crysis 2.
Crossfire performance is still a little wobbly on Crysis 2 and as result the GeForce GTX 590 has a significant performance advantage over the Radeon HD 6990. At 5040x1050 the GeForce GTX 590 was 71% faster, 78% faster at 5760x1200 and 88% faster at 7680x1600.