Advice to replace computer components
 

Please advise which components in my computer it would be wise to replace it with new, so it would be playing COD better-better fps and image quality. Specification of my PC system:

Asus P5N32-E SLI
Intel Core 2 Duo E8400 3678 MHz
socked 775
8GB Memory
Windows 7 pro 64bit
ATI HD 5670 1GB RAM
eyfinity setup 2334 x 1280 (bezel 3x720x1280 + comp.) portrait mode

Thanks for the advice.