I am looking at a temporary upgrade until the fall line of cards come out. I have decided on the X1900 GT because it is much lower cost then the X1800 XT and is R580 instead of R520 and the extra memory isn't much of a concern for me as I run a 19" monitor.
However, I have read some reviews and posts where everyone says go buy an X1800 XT. From what I can see it is 100-150 more and since it is a temporary card (maybe for 4 months) what benefits would I really see?
The GT runs slower but has more shaders, the XT is faster with less shaders. Also are there any hacks that can unlock the other pipelines on the GT? If so then I would likely get the GT and OC it.
Performance wise, they perform more or less the same from what I've seen. The problem with the X1900GT has been the price. It costs much more than an X1800XT but performs about the same. However, NewEgg had an X1900GT for $185. That doesn't help you any though. I haven't heard about any X1900GT unlocks, but that would make the price more justifyable if it did unlock.
One thing that may clear things up about price, I have noticed that the Retail versions of both cards are basically about $50 apart max. But I would likely be buying off Ebay where the X1900 GT goes for no more then $200 where as the X1800XT goes for the full amount of $300-$350.