What kinda performance do you expect from Crysis 2? Even powerful single video card can struggle with the original Crysis at max settings. Meaning under 40 FPS.
Crysis 2 is expected to have slightly lower requirements than Crysis. However, if you want to use Tessellation is which part of DX11, then expect a drop in performance because Tessellation requires a bit of processing power.
Here's a performance chart with some high end graphics cards. The CPU used in the benchmark is an i7-980X Extreme Edition. If you don't have that CPU, then I would say knock-off between 5% - 20% performance depending on which CPU you have.