I had another thread about Powercolor's X800 Pro really being an XT with a different BIOS. I can't remember if it was in that thread, but someone gave a link that had ATi responding to this. Supposedly, they admit that Pros with VIVO capabilities are in fact XTs with a different BIOS, but they said that if the cards are flashed with the XT one, they will fail sometime. Not sure if this is true, and even if ATi did really respond, not sure if they were just trying to put out propoganda so that people wouldn't just buy VIVO Pros and flash them to XTs.
So X800 Pros with VIVO and a copy of Doom 3 (assuming that the XT flash will work and not kill the card) would be quite the deal then.