That varies, some cards allow temperature above 100 celsius, others may shut down at 80. I'd recommend a GPU not exceed 75ºC in operation, it isn't going to be at its best above that temperature.
Ati chipsets fry at 90c not sure about Nividia but it has to be near there. 75c under load isnt recomended. I run a Ati R481 chip (x850 xt pe) at 32c idle and 55c under full load, a chip notorious for running hot. with that card I would shoot for a 60c under full load this can easily be obtained with a 3rd party cooling system for as little as 25 dollars
That's not hot, my GPU runs from 45 to 75, and runs fine at the latter. I would have thought circuitry would fry at that temperature too, but I hear the nVidia management software only shuts down at 120ºC. Obviously nVidia have more thermally-robust chips.
