If you got the money get the X1900 XT. I would recommend agianst getting the XTX because it's only 25mhz faster then the XT, and 50mhz (100mhz effective) more. But that only gets it around 3-6 more fps and for some reason it uses a ton more power then the XT for such little increase in speed.
I would recommend the HIS X1900 XT IceQ III because of the kick *** cooler (MUCH more quiter and cooler then stock heatsink).
Don't get the X1900 GT, ATI really screwed up with this one. It costs more and the 7900GT performs better in most games.
As far as drivers go. I am sick of people saying the ATI drivers for the X1K series are bad. They are not bad, maybe not as good as Nvidia's, but that doesn't mean they suck. Ever since ATI released their crappy X series drivers people keep saying ATI's drivers suck. It's like saying Germany is full of Nazis, which it was back between 1933-1946 but now any Nazis there are a very small minority (there are more neo-nazis in the US then in Germany).
You can unlock 4 extra pipelines in the X1800GTO pretty much making ita X1800XL (or XT I forgot which one). Both the X1800GTO and 7600GT are very good cards but if you unlock the GTO it is better the the 7600GT.
In my opinion:
WRONG... The X1900 is much more than a X1800 with faster memory. ATI found a way to have each shader pipeline to have three shader units (versus only 1 like the X1800). So while the X1800 has 16 shader units (1 on each of it's 16 shader pipelines) the X1900 has 48 shader units (3 on each of it's 16 shader pipelines).