yea it depends if you got a good chip
First you will definitely need to get an aftermarket cooler for the Q6600
Im using an OCZ Vendetta 2 and it was the best cooling solution for the Q6600 at the time that i bought it, i know it ain't that good for other CPU's tho but it was really good for the Q6600 for some reason.
Anyway, i got mine to 3.6ghz with good temps around 60 load and my Vcore in my MB settings is like 1.45 but it doesn't run that high, only like 1.4 when you really use it.
My Q6600 can go higher but temps are keeping me from doing it, i used to run like 3.73ghz 24/7 till i was like alrite its not worth it cuz my temps got into the 70's
With water-cooling i can probably do 4.0ghz flat or 3.9ghz 24/7 but it all depends on ur chip....the G0 stepping are better though for OC'ing and temp control.