Yeah, i thought that might be it, i think whats happening is its throttling back the boost as its getting to hot, getting up to 80c is pretty high, to high.
It shouldn't get to that temperature, unless you live in a sauna... are the fans spinning up properly, have you got the fan speed monitor enabled in MSI OSD? what % is it reading under load?
Boost edition cards have a voltage of ~1.25V as default which could explain the higher temperatures.
AFAIK the cards don't throttle all the way up to 100c at which point they practically stop.
My faulty MSI TFIII card reached 100c in the top slot and throttled down in a Heaven run
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