I have this same problem, and it appears to be a driver issue SPECIFICALLY with FFXIV. The card works fine on other, higher stress games, is not getting anywhere near dangerous heat, and the problem is perfectly reproducible. All I have to do is hang out on that one special uldah server, and about once an hour the driver will crash. Then it will either recover and everything's cool, or it will restart the comp and everything's cool once its back up. This is the most recent driver btw, and has been an issue with the last few as well. I would downgrade to try and find something more stable... but we have a week til the engine goes away anyway, so not worth the effort.

Might be something to the full screen/windowed thing too.