I prefer using 4c/8t am happy at 5Ghz 1.35v! Am testing 5.1Ghz 1.35v now! Run 14 Hard lock up! Notice thou on my 2600k that 1.65V Cpu Vtt Help ocing! Have got some new memory coming at the weekend hopefully that could help! 4GB G.Skill DDR3 PC3-17600 Cas7 2200MHz RipjawsX!