I ran at 650 out of the box, bumped up to 750 a couple weeks ago.

I abused it about as much as I could with daytime ambient temps that hit over 50°C in the mining room and a worst chip temp of 86°C, with chip temps no cooler than 77°C on the coolest of recent mornings.  Average chip temps are 78°-80°C in an abusive environment and it's still chugging away.

The stupid high ambient temps I was experiencing are over now that I resolved exhaust heat issues, but I'm comfortable running these chips up to 80 all day long.
I suspect the guy that blew his up was also comfortable running at 80.

YMMV