BFG announced two flavours of the GeForce 8800 Ultra. Even with Danger Dan water cooling block they didn't go over the reference clocks, but that doesn't mean that it can't be overclocked.
The first one is the reference design, same cooler and same clocks. Second one is more interesting since Danger Dan made a water block, just BFG didn't clock the card any higher.
Both cards ended up with reference clocks, 612 MHz for the core, 2160 MHz for memory and 1500 MHz for shaders. Water cooled version looks good and probably can go higher then air cooled one.
You can get more info about them at BFG.