I am using a Q6600 at the moment. But I only have the smaller intel heatsink that was intended for a pentium dual core E5400.
The temps were pretty high at 2.4ghz, so I changed the multiplier to "6" instead of "9" in the bios, so it only runs at 1.6ghz. But the voltage seemed to be 1.15v.
What do you think the lowest voltage I can get away with is, if I'm only going to run the CPU at 1.6ghz? It says on the intel site that 0.85v-1.5 is the voltage range for this. Does that mean the CPU can be run at 0.85v, if you are only using 1.6ghz?
I lowered the voltage to only 1.00v and it seems to be stable so far with prime95 running, and the temps never get above 55c
as a former Q6600 owner that is a problem even at stock (as you found out).
from my experience; with the "appropriate" stock heatsink, which had a copper core, it would run warm. any OCing would see 50c tamps at idle and 80+ under any load. i can't imagine using an all aluminum heatsink on that.
you will have problems until you get a better cooling solution.
Remember the golden rule of statistics: A personal sample size of one is a sufficient basis upon which to draw universal conclusions.
Upload the computer to Dropbox and provide a link to it so others may download it to examine and give advice for repairs.