They've disabled overvolting in afterburner and you have to jump through alot of hoops to get it working - search engine it and there are guides. In addition, some cards are now voltage locked.
As for the high temps, its possible(but not likely) you got a bad thermal paste job, or have an airflow problem.
80 is really not so horrible. My old 8800GT once hit 130 C and lived to tell about it. My old x1950 used to run regularly at 100C when gaming, 75 at idle. I ran that card 24/7 for 6 years straight - it still works. Modern GPU's can really take some heat. They're usually obsolete long before they burn out. I had a Radeon 9800 pro that I bought back in 2003. That card burned out in 2010 only because the thermal paste dried out and the GPU fried. But now I'm rambling like Grandpa Simpson.
My new 7850 runs at 62 C full load (1050/1300 @1.075v) though it has the XFX double dissipation cooler on it. The XFX Double D cooler models are the only ones now with a lifetime warranty.