SupCom will benefit more from a better processor.
Crysis will benefit more from a better video card.
I'd recommend grabbing a Radeon HD 5770 now if you want to upgrade something, and then save up enough money to ditch the LGA 775 platform all together and spring for an AM3, LGA 1156, or LGA 1366 setup.
You'll need roughly another $500 minimum to upgrade your system to a more up-to-date gaming platform, but it'll be money well spent.
What resolution do you run games at?