I just started overclocking mine. I've gotten to 4.8 @ 1.37v. Temps are about 90 during stress test. I have a H100. I'm not sure if it's stable there because temps were too hot for me, so I shut it down. My understanding too is it's a lottery. I've read a few placed that say the Costa Rica chips overclock better. I'm not sure how true that is. I got my 4770K from Microcenter and asked for one from Costa Rica and they did give one.
I did disable something in the BIOS per the manual. I know that's not much help, but check the book. It recommends disabling a CPU integrated VR fault management setting. page 3-21. Not sure if that helps you...
Gaming/Folding Rig 1: i7-4770K / H100 / ROG MVIF / 8GB 1866 Dominator Platinum / Gigabyte GTX 670 2GB / Samsung 840 Pro 256GB / Corsair 650D / Corsair AX1200i
Gaming/Folding Rig 2: i7-2700K / Hyper 212+ / Z77X-UP4TH / 8GB 1600 Corsair Vengeance / Gigabyte GTX 650Ti Boost 2GB / Corsair Force GT 120GB / Corsair 400R / Corsair AX850