Just one core...

Specs:
i5 3570k @ 4.2GHz
Hyper 212 EVO
Asus P8Z77-V
8GB Corsair Veangence RAM

Okay, so I've trying to get my overclock stable. I think 1.160-1.168v is the limit of stability for me. However when I'm running Prime95, all the cores are able for 12hrs (haven't gone longer) but one. Around the 3-4hr mark, my 2nd core always gives me an error and stops while the other cores continue.
Also, the 2nd core seems to also be the hottest. It's around 65c while the other cores are around 60-62c.

I'm testing again, I've set the CCL to High (50%) and CPU phase control to Asus Optimised. I will see if it happens again.