85 is the highest you'll want to go, to be on the safe side of things. 90 - and it starts to get dangerous.
How are you measuring the activity usage? MSI Afterburner? - You could attempt to use MSI Kombustor's 'furry test thing' to check the usage, temps, etc and see if any tearing, etc appears
AFAIK, there's no reliable GPU diagnostic tools out there