Intel definitely says max Vcore on Q6600 G0 is 1.5V.
I've been playing Fallout 3 with no updates or anything, and don't have freezeing problems. HOWEVER, occassionally the game will freeze when I first start it (crashes prior to displaying Title Screen).
Only other problem I have, is when I Alt-Tab. If I Alt-Tab directly to desktop, with no other windows open, it crashes. However, if I open Firefox first, then open Fallout 3, then Alt-Tab I have no problems.