First the best way to overclock your 760k is to make it through the mb's bios and not using easytune...4,2ghz is very good which voltage have you used ? Normally 1,40v should be enough more generates more heat... LLC is set on auto for me as i've done a gentle overclock with my 5600k (40x100 @ 1,30v --> +0,00v on sniper a88x M.I.T)...Using normal, medium and extreme settings will adjust your cpu vcore better under heavy load since you should know that heavy load downgrades the vcore set in bios: i.e: 1,40v can reach 1,35v or less which will cause instability and bsod as 4,2ghz needs more power to be stable so a high llc setting will "automatically" adjust the right way the needed vcore under heavy load (games, benchmarks...)