Either setup would work, although I'd strongly recommend the XT version. The only difference between that and the XTX is 25Mhz core and 75Mhz memory. The XTs all seem to be coming with 1.1ns ram as well, although this is only guaranteed on the XTX version.
Just flash the XT with the XTX bios when you get it as the cards with XTX bioses tend to o/c a bit better.