Heat spikes ? what cooler are you using ?
Off set works for me.. I think am using -0.035 on my 6600K with an OC of 4.4k ( still peaks around 1.312 V )
Anyways you use offset mode. with the setting on auto. Check what voltage your CPU is demanding. Then change the AUTO setting to 0.25 plus mode. Reboot check if the spikes or lower. Keep doing this untill you crash. Then go back 1 step and you should be golden.
Try more, Try harder, Try and previal