I've got a GTX 660 SC 2GB and it seems to consistently crash my entire system during heavy games (but perfectly stable in desktop).
Basically the temp gets around 80C (and for some reason fan maxes out at 52%) and everything goes black and i have to hard re-boot. Occasionally, the GPU fan explodes to 100% at the moment the crash occurs.
My card at idle is around 40C, 30% fan speed (dual monitor setup, but only use one at 1920 x 1080 when gaming)
I've uploaded a couple youtube videos to demonstrate the problem...
The SC series over the last few generations is the only factory overclocked card Im aware of that the manufacturer uses a reference PCB and VRM.... Asus, Gigabyte and MSI have historically used custom PCBs and beefed up VRMs w/ more phases to "spread the load" and run cooler.
try using Precision or Afterburner to increase fan profile.