Idle temp vs. actually in use, it's suppose to go up, and that range in the OP is excellent, my 7950 when I ran the Heaven 4.0 benchmark, jumped up to as high as 72, but that's still not a problem.
If it only distorts in that one game, it's probably not even your card that is the problem, and once a month glitch is within the range of normal, I would say.
Even so, blown out 3 video cards? You probably do have a heat problem in that case and I'd get some more fans and make sure the one in the back is sucking air OUT and that all the fans are cleared of dust/debris, and check for the video card driver
setting for it's fan, maybe too low or even the BIOS fan settings could be too low and not getting enough airflow.
Could be PSU issue too, if it's more than 3 years old, I'd consider replacing anyway.
Some short in motherboard regulating things, getting a little less likely, but possible.
Any black marks on the motherboard itself or slight burn smell in the case?