You either forgot to use cooling paste or you used too much or too little or its uneven.
The stock voltage is often over 1.4v for those CPU's and prime small fft + linpack draw a huge amount of power compared to other loads; it's possible that it was fine all along.
The majority of overclockers are undervolting their CPU's while increasing clocks; My OC is cooler than full stock out of the box settings.
It's possible that the stock turbo voltages were not really dangerous at all and that it's a mistake to undervolt; there's not much faith in people to set 1.45 - 1.5v on these chips, though. People are a lot happier in the 1.3 - 1.4v region, at least til some crazy guys have increased voltages over stock and been fine.
Stock for me (~1.42v) in prime 8k would probably run at like 80-85c while it sits happy in the mid to high 60's at 1.385v while video encoding with clocks at max possible on that voltage.Edited by Cyro999 - 11/9/15 at 7:01pm