My thought is whether I should get a 7950GX2 or an ATI 1900XTX.

Is it possible to have two 1900XTX's in Crossfire mode? The main game I want to play at first is Oblivion but obviously I will want to play more games in the future and I'm thinking about which card will be good longest into the future and also its potential to be doubled up/upgraded. I've heard ATI cards are better for Oblivion?