The E7400 might hold you back a bit with an SLI setup, but I can't say for sure. Other than that you should be fine. Rather save for a new build than upgrade this one. Socket 775 is effectively dead now.
Most of these games arnt very demanding to play, bar Diablo 3 which we dont know yet, so they should work fine but herr states the Cpu will be the bottleneck if your Sli. And btw, wats with the overkill PSU?