Im just going to guess your having heat issues at 1.611 vcore. Thats right around where I am and I have to try pretty hard to keep my chip cool. I cant bench unless I am running chilled water through my rig. If your trying to do some benching you might want to pull it back I have trouble when ever I idle over 30 at those speeds. With 1.6 vcore the swing is CRAZY youll go from 40 to 90 in a matter of seconds.
Oh yea and if vtt is the same as uncore I keep mine just under 1.5