The OCCT stability test sucks(the 30 minutes one). Use the torture test. I've had a cpu pass the 30 minute stability test, but fail the torture test in less than a minute.
Prime95 takes way too long to crash just when you think you're stable. OCCT is good for quickly finding a speed that's just too high, then backing down slowly until it runs stable for a few minutes, then hours, then run your Prime95, etc.