I got a fan doing 1500 RPM. I installed it in the mid-rear and it does like, nothing. CPU and stuff seems 2° colder but thats all.
If I'm running guiminer I get 110°C and the system crashes.
Looks like a broken card...
Try re-seating the HSF, and use good TIM!
Unless you have 100°F ambient temps, there is no reason why any card should be running that hot at stock voltage! If you are excessively OCed, there is your problem! If not, it sounds to me like the HSF is not FLAT on the GPU die, or your GPU fan died!