Quote from the review ay Hexus.net:
“Currently, NVIDIA state that a 6800 Ultra is a full four quad NV40 (AGP part) running between 400 and 425MHz, with 256MB of GDDR3 memory running between 1100 and 1200MHz on a 256-bit memory bus, with a pair of DVI ports. Any 6-series board that meets those specs is a 6800 Ultra. Any board that comes clocked higher is able to be called an Ultra, according to NVIDIA’s marketing specs, but the GPU shipped to them by NVIDIA after sale is only warrantied up to 425MHz.
The GT is defined as a full four-quad NV40 (again, on AGP), running between 325MHz and 350MHz, with 256MB of GDDR3 memory running at up to 1000MHz on a 256-bit memory bus, with either dual-DVI, or DVI and VGA. Meet those specs, call your board a GT according to NVIDIA’s marketing specs. Anything over that spec is a partner-defined board that may or may not be allowed the GT moniker, since it potentially impinges on the basic Ultra spec, depending on the DVI port configuration.”