A 6800 Ultra may not reliably drive two of them. I would absolutely inquire with the manufacturer before purchasing. I have a Dell 24" (2405FPW) and 20" (2001FP) that I have connected to a 6800 Ultra, both via DVI, and the 2001FP loses connection from the card randomly for a very brief moment. The vendor, BFG Technologies, said that the card does not officially support two DVI connections at the resolutions I was running (1920x1200 and 1600x1200).
YMMV, but definitely consult your video card manufacturer for the definitive answer.