I recently overclocked my Q6600 to 3Ghz. It was stable as far as I was concerned; 1 hour OCCT, 20 passes on IBT, and 8 hours Large FFT's on Prime95 with no errors.
As a last test I then decided to run memtest86+ which found errors almost straight away. I upped my DRAM voltage gradually up to 2.1v (from 1.8v stock) but was still getting errors. I found it a bit odd that I'd need to pump so many volts into such a basic overclock so I decided to put everything back to stock and retest the ram again.
I ran it for 8 hours overnight and ended up with 12 errors over 7 passes. Testing one stick at a time finds that I do indeed have a bad stick of RAM.
The thing is that I've been running this system for over a year with no problems at all. No BSOD's, no errors or reboots, nothing. Is it possible that memtest is simply wrong, or should I go about getting an RMA?