After being sick of running Crysis with a low frame rate, I decided to look around for something to improve performance whilst maintaining a frame rate above 20 frames. I stumbled upon Cuban Ultima Doom Arch Assassin Taowolf Sword's Custom Crysis Config v2.21
This config contains 6 levels of quality and an improved ToD (Time of Day) which adds more realism. To anyone who has Crysis this is a must as it really does improve performance and image quality. (For those who also have Warhead, there's an optimizer on that page).