IMO, it's not worth the extra money. I doubt the differences in FPS and eye-candy are noticeable. And if you overclock, I've heard that the 9800 Pro can be OCed to XT specs.
The only differences I can think of between the two (except for the obvious increase in core/memory speeds of the XT) are the Overdrive feature and the built-in thermal sensor on the XT.
But, the 9800XT is currently top dog of video cards, and I'm willing to bet that John Prophet will tell you that chicks dig it!