If you don't play anymore then 10x7 resolution I would get the X1900 XT, don't bother wasting money on the XTX because there is very little difference between the two, ATI should have just made one.
Get this one, it has a better cooler which makes it cooler and quiter.
I was going to get one of those, but now that I got one of these:
I am starting to think about getting the 7950 GX2 just so I can play games at the insane 2048x1536 @ 85hz. I never recommended the 7950 GX2 mainly because most people don't have monitors that go over 1600x1200, most are stuck at 1280x1024 because they use LCDs. Unless you have the ability to play with these ultra high resolutions going SLI or dual GPU at the moment isn't a very good decision, this is mainly becuase of CPU limitation. In games like HL2 the 7950GX2 performs a lot like the 7900GTX when played at 10x7 and 12x7 resolution. So unless you play at 16x12 and higher you won't see an incredible boost in performance. However some games that eat up frames per second like Oblivion and FEAR, having a multi-GPU setup will help quite a bit.
To put it blunt however, it isn't worth buying SLI, Xfire, and dual GPU setups if you don't have the means to play something higher then 12x10 resolution. Your better off just buying a X1900 XT.