Running software only programs like RC5, Seti, Prime95, CPU Stability Test, etc., does not always cause my overclocked system to crash.  I had my Cel. 566@850 running @ 1.80v and I could run RC5, Prime95, CPU Stability Test for days on end and it would never give me errors.
I even ran a Q3 demo loop for about a hour with no lockups or crashes. 
But with UT being the overly CPU dependent game that it is, I could not even make it through one loop of the startup demo before it would give me a fault. Not a problem with my video card or RAM, I just had to bump the voltage up to 1.85v.  Remember all the above programs (RC5,Prime95, etc.) would run fine.
Compuwiz is right about 3DM - I still get random crashes when using it too.
If you have UT, try running the default demo loop for 15-30 minutes or just try to play the game with several (6+) bots. If it hangs up continuously, then its not stable. If it does not, then I would say your system is good to go.