Why hasn't anyone asked for temps? What are your temps? Use HWmonitor or a similar program to get temps. Speed fan will also tell you. Note idle temps and when the fan starts to rev up. If its getting to hot you could also have some thermal throttling which reduces performance. To test the temps at 100% load you can use Prime95 (blend test is fine) for atleast 5 minutes and that will get you your max cpu temps. If at any point during any of the testing the CPU goes above about 67c thats a good indicator that you need to reapply thermal paste.
As you are using a stock cooler with a stock cpu non overclocked it should be sufficient.
Edit: aw guys. I was typing as fast as I could
. Beat me to it.