I'm not sure about this. Yes Prime95 is good to test stability but it doesn't seem to need as much voltage as IBT - I am not using any LLC and am using offset. I had set the offset so that when running Prime95 voltage dropped to 1.12v at 4.2ghz and this passed a 22 hour run. However when running IBT or x264 the voltage dropped further to 1.112v causing whea warnings to appear. Then the penny dropped that voltage decreases proportionately to load when not using any LLC. So I upped the voltage so that when running IBT / x264 the voltage did not get lower than 1.12v. No more whea warnings.
I think Prime95 should be used as one part of a stability testing strategy, not solely.