did you clean off the factory thermal paste pretty well? everything tight and secure?
It takes a few hours for the AS5 to properly settle, but it still sounds way high 80C.
I use a Cooler master 212 EVO and AS5, run prime95 for hours, temp never went above 65C on my i5(stock clock rates). that's with my room temp ranging from 77F to 84F. (warm room, I know but I had make sure the cooler was worth it)