There isnt such thing as a X1900GTO but if you got them the wrong way round I would say the X1900XT is better because its much faster and had more pipelines!
Not yet, but its set to be released the begining of this month in the US so maybe mid to late May here. Google it.
ok cool... it looks like ATI is taking over the GFX world!... Back to the subject, if its got more than 16 pipes and its faster than the x1800xt then yes, its better!
Yes there is, The 1900GT/O is replacing the X1800XT. So the lineup will be: X1900XTX X1900XT X1900GT/O I believe it still has 16pipes, but unlike the x1800series it has more shaders, but compared to the 48shaders on the X1900XTX i believe it will be roughly half that.