Let me give you some advice. Prime95 does not stress your CPU out enough. I use Prime95, but I always use Intel Burn In Test so I can see what my TRUE highest temps really are. Prime95 runs about 10-15c cooler than IBT. So if your temps are 70c average, if you run IBT your temps will be 85c average in reality. So to really see if your too hot or just right, you absolutely need to run IBT. Anyone will tell you this.
And yes, as the above poster said, run IBT for more than an hour. Usually around 4 hours will tell you if you stable. Personally, I run IBT and play a game at the same time. That's the test of a true overclock though. Be prepared to fail that test if your not stable just a little bit.