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#441
If you're going to OC to 4gig you need to manually set the QPI/Vtt voltage. Voltages that should be set manually are Vcore, QPI/Vtt, RAM.
For my 3.5 OC I have a QPI/Vtt of 1.215. However visiting Tweaktown's GIGABYTE forum for example, most users have a QPI/Vtt of 1.3 - 1.315 for 4gig+ OC's. It could be less (if you're lucky) but it's mostly around the 1.3 mark.
You might want to visit your MB's forums, or other overclocking forums to get some good ideas on voltages.
Good luck.