I doubt you'll see more than 1c difference with AS5 unless the thermal paste you have has lost it's thermal bond.
80c isn't hot by graphics standards. I had a 9800GT that idled at 90c.
I took it apart and reapplyed the paste with AS5, your right, there is only a 1C difference. Okay I'll guess I'll just deal with 80c, but the thing is it was at 75c before, how come at max it increase 5c?