Are you planning to buy your X1600 online or retail stores?
If online, post the link of the product(s) and i'll indentify it for you. Or, identify it yourself by reading the useful description below it. Same goes with the desription of the retail stores.
Surely, The XT has always been better than the pros. In my experience, the XT's are more expensive, better performance, and maybe more jacked up. (with cool + HUGE fan =D) About the memory having 512, again, read the description of the material your buying. Use google and go research for it.
I hope this helps!