DON'T RUN KILLER DONUT EVER AGAIN.
FURMARK IS NOT GOD TESTED. IF YOU WANT MAX YOU COULD USE FURMARK BENCHMARK NOT STRESS TEST.
For any temperature test you should open side panel install card and start Firestrike, 3DMark 11, Unigine Heaven or even better games...
Fan on 70-80% manual and open side panel. Than you will know real temperatures of your card.
Manufacturers of graphic card can't do nothing to graphic card so powerfull and naturally hot stay cool in closed case, nothing.
Simply such cards need very big case, at least 4-5-6 very good 120mm fans only for single card to cooldown.
Imagine how fast spin 2 fans from graphic card, 2000-2500RPM, they blow 80C constantly, how much 120mm fans need to work on 1500RPM to compensate that... Many of them, it's not even possible.
Every temperature result you look on net are tested in these conditions...

You can install same, set manual on 70-80% and check temps, I can bet results will be 15C or more lower temps.
Off course some things could help you lot, as Vsync... I don't know how that work with AMD, but with NVIDIA very good, and why card to work on 99% even in games where reach max fps on 60% usage... that's 10C less... And if she can't provide enough fps than she will work on 99% anyway.
If your monitor is limit on 60fps why to leave card to give you 150 constantly...