Well considering your performance is nowhere near the norm for that setup, there's obviously some conflict or another. Don't take that as offensive in some way, this is PC gaming, as I'm sure you know.
Crysis is probably one of the best games ever made, certainly one of the best FPSes... don't just give up on it because of something that is fixable. Check out the tweak guide at
www.tweakguides.com and see if it offers any other answers, or post in a real gaming forum and see if anyone has good suggestions.