What CPU cooler are you using? I was using stock air for the longest time, 4.0ghz @ 1.35v would be stable for everyday use and gaming on my i5. Prime would fault a thread every now and then unless I was @ 1.4v.
Just
installed a Corsair H50 last night which dropped the temps a shitton (obviously over stock). I've pushed as hard as 1.475v to get 4.2ghz stable and temps were still under 80c in Prime and IBT.
Personally tho, I'm sticking to 3.6ghz @ 1.3volts. I'm done with posteriety overclocks, these i5/i7 builds are PLENTY fast asis.
Just need to sell my kidney to add a
SSD raid setup...