Room temp 18deg C (reported by digital desk thermometer)
Motherboard: 25 (as reported by BIOS)
Ambient: 33 (as reported by driver)
I sampled the 3d temperature by leaving the temperature display on screen and exiting during the GunMetal2 benchmark at different times. That was the highest temp I saw. I get similar results in 3DMark2003.
Note that the room temperature is low because it is winter here, but you can directly add to that to simulate summer, so a hot summer day could be +20degC, and time to run air conditioners or room fans at gale force.
Also note that the GPU cools very quickly. Eg. within 1 sec it drops from 64 to about 48 deg, then over the next few seconds falls to 41, then slowly cools back to its 2D speed.
GeforceFX 5800 (non-ultra) @ 470/940
Athlong XP 2100 (Palomino)
Epox 8RDA+ (nForce2)
Lots of Case fans.
Note the 470/940 speeds are nice and cool. This card will run stable at higher speeds and run 99% stable at 490/980 with default cooling, but can soft crash (eg. exit app and continue) if running for many hours at that speed. Also, at that highest speed, the fan speeds up as the GPU gets over 80degC. I got it to 90degC repeatedly running 1 particular benchmark at those near ultra speeds. This card won't run at ultra speeds with default cooling.
BTW, the GPU and the board should be rated well over 100degC before you start doing physical damage to it. The computer will show visible problems and crash before you physically damage the card.