Edit:
There's been more than 1 response saying the downclock works. I stand corrected and it must have been due solely to my copy of the XFX card. The engineer I spoke to may not be in a very experienced position with the GTX 280 to identify whether its the card or the series at fault.
Guess it works.
That guy sounds like an AMD/ATI infomercial though! It almost sounds too good to be true, but I'm rooting for the underdog here... hope it is true