my q6600 needs around 1.3625v in the bios to do 3.26ghz, others ive seen are similar. to do 3.4 on mine I need 1.39v in bios. q6600 like a gtlref of around 0.63-0.65 with a balanced vtt. whatever vcore you set, aim to get vtt close to it, higher preferably. if you do that you'll find that 0.63-0.65x should be on the mark. 1.39v in bios for me i use 1.38-1.40v vtt at the sensor. if you aim too low with vtt you wont have enough gtlref adjustment, this is the way it works with 65nm chips.