Crysis 2 uses a development of the Crysis Warhead engine optimised for efficiency but adds DirectX 11 support via a patch and this can be quite demanding. As, for example, with tessellation, implemented abusively in collaboration with NVIDIA with the aim of causing Radeon performance to plummet. We have already exposed this issue here
We measured performance with Fraps on version 1.9 of the game.
The GeForce GTX 680 in SLI is almost exactly on a par with the GeForce GTX 690. The Radeons are however in front at 2560x1600.
At very high res, performance levels between the cards are similar once again.