I know for a fact it has to be my heatsink because i turned it 90 degrees this time when i changed motherboard and i get the exact same tem variances between cores. The "outside" cores run around 10C hotter than the "inside" cores, so the only thing i can determine is that the middle of the heatsink makes better contact than the outer edge. I'm guessing i actually have a flat heatspreader on the cpu, but a convex heatsink.