Yeah, RC5/SETI/Prime95 are all excellent burn-in programs, but I have found that UT is one of the best tests for overall system stability. With my C2 633@950, I could run RC5/SETI/Prime95 for days on end at the default (1.7v) voltage. However, the intro flyby demo in UT would not even make it one loop without crashing back to the desktop. On the other hand, I could run Q3 all day at the 1.7 voltage.
It took a voltage bump of 0.05v to 1.75v to make UT stable.
I think it is safe to say that if you can get UT to be 100% stable on your overclocked system, then all of your other games will run just fine with the overclocking.
Hope this helps . . . .