This chart tends to be pretty accurate; http://mark.zoomcities.com/images/gfx/GFXpowerchartby3d...
It collates information from all the reviews of various cards that can be found online. It's sorted by max power used under normal operation. The extra dark red sections represent power draw under extreme load during stress testing and isn't available for all cards.
Actually the 5770 uses 61.2W on games & 81W on FurMark, however the 5670 already tops the 9800GT Eco, so ATI has little to worry about.
One thing I am interested in is the FurMark test, the 5750 uses 60.6W max their, so it's already quite under the 75W limit.
Now like I said, 81 watts in Furmark for the HD5770. If we take the clocks down, say, 20/30 on core/memory, we might be able to get a Green edition of the 5770.
Not to mention the stress Furmark puts on cards is unbelievable.
Well - I was a bit worried until I kept digging. So far I'm fairly convinced that if I used a good driver cleaner to ensure the NVIDA drivers are cleaned up, and I use the latest ATI drivers I'll be okay. Perhaps a bit of clock tuning, but I doubt it.
If it comes down to it, I can swap the cards back until the drivers are absolutely solid.