Get the eVGA 6800GT. Its really easy to overclock to Ultra speeds because of the larger heatsink.
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 )