Some threads going on other forums at the moment about people that have successfully soft modded the current batch of Club3D X800 Pro Vivo cards to XT by flashing with a Gigabyte Bios.
These cards are shipping with the 1.6ns Ram, bridges still intact and even have XT stickers on the HSF - by all accounts they are effectively XT cards with 4 pipelines disables in the bios
Getting one myself tomorrow to have a go