br3nd064 :
As long as you stay under 1.5v you're good.
Yep, Q6600s tolerates very high voltage. It's one of the reasons overclockers like them. Check Intel's website, their official recommended voltage is up to 1.5v, compared to 1.3v for lesser chips (q9300, etc). As long as it's below 1.5v, safety is guaranteed. You can usually go above it though, like how ocers overshoot the lower limit for other cpus. It should be okay as long as it's not too much over limit.