I've double tested this, OCCT loads 99% but Prime95 hovers around 75-85% mark...?

Ok, what is the best way to test the northbridge for stability? Same as ram, Memtest86+? Or is there something I can specifically use to stress it? I seem to need 1.85v on the northbridge (bios max, actual is nearer 1.9v) to get 475MHz stable with 4 sticks of ram... THAT IS INSANE!!!!