If you want increase in performance you could snag a cpu cooler oc the processor which is rather easy.
For load speed you wanna get an ssd 60gb will be fine just rotate the games you play the most.
And to play the best games upgrade from what you have to something like a 7950 which can run most games on ultra. Your card is getting avrg frames in bf3 for that card, so grab an upgrade you should be running 60+ frames. Sli is an expensive option that isnt supported by some games you would be better off with the suggested card above. Also sli is a *double my fps* option it would marginally increase it. If you want physx grab a 660 or 670.
Those are my recommendations glhf.