Depending on how high the res is and AA/AF and other things like that, a GTX can be brought to it's knees, but obviously not very often :).
Yea, an X1300 would be the worst move every, hardly any games can be played at max with that, I started to struggle with an X800XTPE which is miles better than any X1300,1600 series of cards, the lowest possible I would go to is an X1900XT 256mb, there very very cheap now.
I have found that when buying an 8800 series card, its mainly for DX9, I really dont think there going to work well with DX10 and there will be something new out by the time DX10 hits, god help people with lower end DX10 cards than a 8800series.