What kind of power usage are you seeing at 406.25MHz? That's amazing how your miner is stable there - none of mine seem to be stable even at 375MHz.

I've got one that can run at 406 but the power draw is around 420w. I run it at 400 and another at 393 and together they use just over 750w.
That's not actually too bad, I thought power usage would be higher. Considering my S1's do 180GH/s @ 385W, 420W is very reasonable.