I'd start by downloading a temperature monitor. I use Realtemp. You can tell a lot from how hot your CPU is getting under stress from each stress test especially if you're not overclocking.
Here's a few I use to test overclocks:
HyperPI - Test your CPU's quickness really. It'll get your temps up a bit.
Cinebench - See how fast you can render and such, not much to it.
Prime95 - Of course. I run Max FPU test and the blend test. Check your temps.
OCCT - Good one for testing overclocks, you might wanna check that out. Temps skyrocket.
HDTach - Testing software for hard drives. Cant remember ever using it but its there.
My favorite way of testing stability is doing what I love most. Play an intense game like Crysis or Fallout 3 or New Vegas. Check for crashes and studdering. Real world testing is always good!