I'm going to go out on a limb and say that I don't think the Q6600 can go much over 3.6Ghz on air 24x7. If you have water cooling, that's a different story.

After looking at the 45nm quad core overclocks I was suprised to see less than impressive results from the die shrink. It looks like we will have to wait for Nehalem or future revisions of the 45nm processor.

That being said, even the lower Q6600 VID's (1.20-1.225) don't seem to overclock as well or much better than higher VID Q6600 GO's.

For the average overclocking using air, 3.6Ghz 24x7 is a significant accomplishment.

4Ghz for water cooling is a good overclock for a Q6600 in the mid 1.5v range 24x7. A lot of people here quote their bios vcore instead of the actual Vcore that CPU-Z is registering. This makes it difficult for readers to truly understand the overclocking limits of their CPU's as well as others posting.