no, GT can run at ultra speeds, to tell you the truth, my plain 6800 has 16 pipes (soft modded) and it's core at 420mhz and DDR3 at 1.1ghz. My card even runs faster than some Ultras it seems.
Sums it up right there. This has been discussed a million times. Brand...eVGA 6800GT...they put the same heatsink on all the cards, which means you get a heatsink meant for the Ultra on a lesser card....almost like getting a free aftermarket heatsink. It takes up less power and like they said easily overclockable to and past Ultra speeds.
Conclusion: Hell no the Ultra isn't worth it. ( had a friend buy one, yeesh, what a waste )