This card already comes overclocked.
First do some stress testing and see where the temps peak at in order to determine if your PC case environment is sufficiently airated to support additional OC. If your temps are high, start with cable management. If it doesn't help, you will need watercooling before you can conceive of putting your card through such barbarism.
And I also don't think it will do you much good. Your CPU is at the borderline of being bottleneck.