Something you might want to try is a positive value for GTL's.
I ran the correct values for my setup -50 or something like that and coudnt get 2 cores stable.
Adjusting to a positive value
ie +30 +20 +20 +30 got my chip stable fast and allowed me to lower PLL to its min, and vcore was also lowerd 2 notches.
Not saying its going to work but its worth a shot?
Bookmarks