Should be fine.
I can run the original Crysis very well at 12*10 (4xAA) everything on max (only shadows and physics down a notch). I think Crysis will use all 4 cores of the 6600, plus the 9800GT is faster than the 8800GT (a bit)
ALSO, the engine for warhead has been optimized.
So long as you're not expecting 25x19 8xAA or something, you'll be LAUGHING!