I wouldn't say that there is a huge difference. It would probably be noticed when running the top shelf stuff at the highest settings, but for "normal" people it is barely there. If you are hard-core go for the XL or XT. I've been running a Pro for about a month now, and it meets my needs and then some.
well not really but if you want a champ of a card.. You could try maybe...for instance try a 6800GT.....Just pm me for more info and I will lead you the right way....
I got a decent 440 core and 550 Mhz OC out of my new X800 XL . Honestly? You'll never actually see the difference in a real life game. The prices on the XL's just dropped about 50 bucks across the board recently.