I have my PII 965 set to 3.7ghz @ 1.4125v and its idle and load temps are roughly the same as stock speed.
Idle: 30-31C Intel Burn Test 20 runs: 55C
I ran 20 runs of Intel Burn Test and it didn't crash. I hear people like to run Prime95 overnight or even longer, but I don't intend to do that. Heck, I don't even intend to ever have my computer on longer than 24 hours...
So, what are some other ways to test for stability?
More abouttesting stability
try OCCT for about 1 - 4 hours and see what happens
Prime95 for 2 hours and Crysis Benchmark for 20 loops on the highest settings are what I use. Never failed with them .
Oh, also 3DMark if you can.. I know of people who just use 3DMark Vantage / 2006 to test for stability.