For ya quad 1.2 HT is very important plz up to 1.5 at least to be stable , my quad also needed 1.5 CPU VTT to be stable at 425FSB, 450 needed to need more... but never got that one stable...

also the Arctic cooler doesn't cut it with quads mate , better get somehting beefier going, what are ya temps at 3ghz under Prime ?

1.2v HT Voltage: 1.25 --> 1.5
NB Core Voltage: 1.45
SB Core Voltage: 1.55 --> 1.6
CPU VTT Voltage: 1.40 --> 1.45