It actually looks normal to me. Crysis is a very GPU intensive game. If you want to get a higher increase in FPS, I would suggest turning the AA and AF down, because that is what kills it.
You can turn all the other visuals up to give you all the eye candy, but the AA and AF is what slows it down because it is a lot of graphics detail to render. I have around the same FPS, maybe a bit more with an HD 5870 and an i7 975 @ 1920x1200. So you are doing fine.
If you want to get more performance out of it, you can try to OC the card if you know how, or you can get another GTX 285 and a bigger PSU, which will cost a pretty penny.