Re: multiple monitors, higher GPU temperature
Switching the memory clock causes flickering on one of the attached monitors if there are two or more monitors connected. The problem is common not only to linux and windows, even AMD and nvidia share this behavior.
The "solution" found by the graphic card vendors is to allow only the performance mode with the highest memory clock and a somewhat lower than maximum GPU clock as idle mode, if there are two or more monitor connected.
But 85° is high, I think your card and possibly your case has bad cooling. What happens if you run furmark or something?