varis :
Why do you want to upgrade? Is the performance bad? What resolution do you play with?
I'd wait until you start being dissatisfied with performance, then follow the advice above.
^ Very good point.
Usually, if gaming is your thing, look first to your graphics card for an upgrade.
1) Run your games, but lower your resolution and eye candy.
If your FPS increases, it indicates that your cpu is strong enough to drive a better graphics card.
2) Lmit your cpu, either by reducing the OC, or, in windows power management, limit the maximum cpu% to something like 70%.
If your FPS drops significantly, it is an indicator that your cpu is the limiting factor, and a cpu upgrade is in order.
It is possible that both tests are positive, indicating that you have a well balanced system, and both cpu and gpu need to be upgraded to get better gaming FPS.