based on what I can see there,
I would say upgrade graphics card and overclock your chip a touch
check your current set up on http://www.yougamers.com/gameometer/10213/
though for the different crysis games, see what it shows you
the 5870 is a better card, and if you do look at a new chip, the 955 will tweak easily past the 965 for a cheaper outlay.