If you have a Hawaii card, I urge you to crank power limits down in the overdrive tab of CCC and see what the resulting clockspeed is under full load. Even in a worst-case scenario, I'm seeing a typical clockspeed of 850MHz with the slider all the way to the left at -50%
That means that Hawaii (the two samples I personally own, at least) can run at 850+MHz on only 145W (half the 290W TDP). As mentioned, that's a worst-case scenario using a power-virus like Furmark. Under real gaming situations (I was messing around with Alien Isolation on 1440p ultra settings) the clocks averaged about 925MHz yet my PC was inaudible; Fans that normally hum along at 55% were barely spinning at 30% during my gameplay.