Yeah, it's heat mostly. Depends on your cooling system, I know my system runs pretty cool for a gaming laptop, so I OC'ed it a bit for fun. I got a stable overclock from 2.16 (original) to about 2.4. After that, Windows was fine, but 3DMark06 wouldn't run. I chickened out at 2.5, in which Orthos wasn't posting errors, and everything except 3DMark06 was fine.