You can overclock your cpu if you don't want to upgrade. If I'm not mistaken the E6xxx cpus could reach 4.0ghz easily, that will certainly provide a great boost in performance.
Also, I have a GTX550Ti (Rma upgrade from a 8800gt) paired with a Q6600 @ 3.2ghz and it has served me well considering I game at 1680x1050 resolution. You'll be able to play all the games you like easily at that resolution (1600 x 900), even if a bottleneck exist with your CPU. Some people use the term bottleneck as if it makes the game incapable of running at all.