Flashing an HD7970 for <225w 2.5GT/s mac pro 1,1 use, help please

absolute maximum power is 225w (I think, it's a 1,1 so maybe less) and the PCI-e is limited to 2.5GT/s so the card is wasted set at full potential
whats the deal there?
bios editing? I've never done that
or just use an HD7950 bios?

AMD windows drivers are awful, EVERY resolution is SCALED!!! terrible.. Any fixes for that?