Yes, in deed that is getting rather toasty. And I thought my HD4870's 50 degrees was over doing it. Look into your airflow, as mentioned above. Also, what I just did, was replace the thermal grease on the card's heatsink assembly, and it made a world of a difference (dropped my idle temps by about 8 degrees). As I found, the thermal paste had dried up from being on the shelf so long (the card was probably on the shelf or in the back for well over a year now and with room temp changes and humidity levels changing throughout that year, it probably caused the thermal paste to dry up on my card).
Anyway, just be careful you don't damage the card remvoing the heatsink. At least on ATI video cards with moderate coolers, it isn't all that hard, and only takes 5 minutes of your time and some good thermal paste. If that doesn't help, look into better air flow in the case, or maybe a different GPU cooler, if your setup allows such a thing (they can get rather bulky and heavy).
Are your CPU temps also high? This would be a tell tale sign it's not just a GPU problem ,but more likely an case airflow problem.
And as for the PSU, I don't think this would affect the temps as much as performace or crashing. If crashing isn't a problem, then the PSU is probably fine... generally a video card corruption generally will occur more from heat before it becomes a PSU problem, because if it was an issue of lack of power, the PC would reboot or crash during game playing. I do agree that less than about 600 watt for an SLI/CROSSFIRE setup (even if using a reputable power supply) is generally asking for trouble, unless your using moderately low-end cards that don't use as much power. but even then so, more power is generally better to a point in terms of multi-GPU configs. The fact that his card can run at 99% and supposedly doesn't power off or reset the system makes me think that the PSU is not an issue in the case, unless your PSU sits right next to your GPU or somehow blows hot air onto your video card. It could technically increase case temps, but I don't think it would be enough heat to see what he's seeing as far as GPU core temps, unless there was little or no airflow in the case. Even a case with an intake fan and exhaust fan should move a good portion of the heat out of the case ,providing that you're using large enough fans (80mm or larger).
A slightly cheaper alternative might be to get a slot cooling fan and put it near the video card. This helped me some, but again, it comes with a cost of generally creating more noise. So you have to weigh that one out too... a new coole ror more fans. In many caess, a better cooler with better air flow is better in the long run (for your hardware and your sanity---unless you're immune to fan noise).