The game kinda annoys me, I am running it in my rig below (E8400@3.7, 8gb, 8800gts 512 etc...) and I can run 70% of the game at 1680x1050 everything high and have awesome frame rates... then you get to that dumb sphere and it's all downhill for me. For the last bit of the game I had to reduce my shaders and shadows to med quality to get acceptable frames though it was still not smooth.
I did finally add that config file which loads all the textures into your memory and that seemed to help a little at the cost of longer load times. At one point my system had almost 4gb of physical ram usage!!! No idea what portion of that Crysis was but I'm sure it was most.
I was not a huge fan of the last part of the game but the first ~70% was awesome. Simply a freaking pretty game!