Does that board have the latest BIOS already? I know it's a different platform but my buddy bought a ASROCK 990FX Extreme 3 and the BIOS it came with was horrible, glitchy, wrong readings. He didn't have a thorrtling issue but just the BIOS was crap. Since then he has flashed to the latest one and although I still think it could be better, I will say it is WAYYYYY better. So perhaps that's something you may try.
I will say, 4.5 GHz stable does sometimes take some vcore. I just ended up leaving mine at 4.4 GHz. 4.5 GHz was stable for me when running my RAM at 1600 MHz, but now that I have it at 1866 MHz, I just backed it down to 4.4 GHz.