This issue is very random so far.
Two identical setup, one user may constantly hit this high fan speed bug. The other one may be completely unaffected.
From my experience, flash of not won't affect the result. I met this bug before when I was using the genuine Sapphire HD7950 Mac Edition card. From memory, I can hit this bug even with the stock HD4870 as well.
That's why I end up study the SMC key, and make my own version of fan control software to let the fans do exactly what I want.
The base file in the ROM that's been identified can probably be used to change default fan behaviors, possibly voltage as well for tweaking memory voltage to accommodate for DDR3L 1.35v modules.
One more thing... what slot do you have your video card in? I’ve noticed the higher fan speed issue with a 4,1 logic board with the video card in slot 2.