The bottom line on the GIGABYTE 6800 Ultra is this, if you can find a card in this price range and want to play Doom 3, go for it! This card and the other 6800Us will give you the best experience in that game currently. This might change with updated drivers or with new product releases but honestly, at the moment, NVIDIA cards are the best for Doom 3.
I, however, don't buy a video card for ONE game. In the three games I tried with the GIGABYTE 6800 Ultra (Far Cry, Joint Operations and Thief 3: Deadly Shadows), I had no issues with playing the games at maximum resolution and IQ settings (1280x1024, 4x AA, 16x AF) that my monitor supports. As such, it's a perfect card to play those games. As I don't have a X800XT PE, it's hard to recommend a card I haven't tried, and so I won't.
I almost gave this card an Editor's Choice award. In my time with the card, it's proven to be silky smooth in everything I've tried it on. The bundle just adds to the value of the card. Thief: Deadly Shadows is a fun thought-provoking game. Joint Operations is a great multiplayer game that was what Battlefield Vietnam should have been in my opinion.
Downsides of the card are few and far between. First is the cost. Quite frankly, I don't like to spend $500 on a video card. Second, availability is an issue with all GEFORCE 6800 Ultra cards. There are three stores on Pricewatch with this card in stock for as little as $539. Be careful out there. With the results of the card on Doom 3 being shown, there are cards retailing for $100+ more than the MSRP. Just the other day, for example a 6800 Ultra Extreme Edition went for $1125 on Ebay. The second possible downside is it'll be unlikely that SM 3.0 will be used in games prevalent until 2005, or more importantly, have a visual difference between a game using SM 2.0 and 3.0.
