I was running it at 770 core and 1100 memory (as I recall). I'm not sure of the temp. I never heard the fan ramp up so I assume it was still quite low. I literally only ran the card for 10mins before I got artifacts. I've tried loads of different drivers but no dice. I think it's toast
It sucks because my trusty 8800GTS has never failed me and it runs +20% clock speed 24/7 for 2 years and no problems. I've never heard of clock settings damaging anything but maybe it is just coincidence.