The G80 GPUs have been tested by NVidia to operate at temperatures near 150C, but I am unsure when the core slowdown threshold is met on the 8000 line. I can assure you though, unless you've removed the heatsink or have an incredibly cramped case with minimal airflow should you be concerned about reaching that temperature. The CST differs from GPU to GPU, but it usually hovers around 125C or so, though I reiterate that only under extreme cases should you find your cards at this temperature.