Here is my test report:
EVGA 6800 Ultra, with that fat Zalmann all-copper cooler.
The card is fast enough for my taste, but the thing that was nagging me most was the power consumption when in 2D idle mode. The card takes a lot more power than my 5900XT, when doing nothing. The GTU BIOS lowers the voltage in 2D, so it should help.
The GTU BIOS lowered the idle-mode power consumption from 150 to 144 watts (complete machine before PSU).
Loaded wattage for the whole machine went down from 262 to 252 watts with the default clockspeed, temperature went from 74 to 70 celsius.
However, default clockspeed means that the GTU BIOS has lower clockspeed (although better RAM timing), so my Doom3 FPSes went down from 52.9 to 46.8.
When trying to clock back to normal Ultra speed, I had to discover that the Linux "nvclock" program doesn't work right with the GTU BIOS. Any change in RAM or GPU clockspeed would slow the card to a crawl (around 5 FPS).
I put the old BIOS back and the "nvclock" program works fine with it. I don't get useful overclocking speeds out of it with the standard Ultra BIOS, so I am back where I started at default speeds. Depending on how that Zalman and the Ultra live through my non-A/C summer I will probably clock it at Ultra Extreme speeds, though, at least when there are heavier games coming out.
The Zalman cooler rocks, though, highly recommended, it shut up the card real good, and lowers GPU temp by 3 degrees C in the high-RPM and only raises by 4 degrees C in the low-RPM mode. I just don't understand why they don't interface with anything where you could switch between high and low from software.