On my Duron 800@1000 using Prime95 I get "hardware failure" and then it stops. But I have run Rc5, seti@home, and played CS,UT,D2, for hours on end without a single lockup. Just the other day I ran Rc5 for almost 15 hours straight and it was still cracking. Then I played 2 hours of UT and ran smooth. Sorry to rant... anyway all of the forementioned programs would serve you well.