I think the order is x1300pro < 6600 < x1900xtx. The 1300 and 6600 will be close but I'm pretty sure the 6600 is faster. The 1300pro should be like the 6200? Probably sits between the 6200 and 6600.
Exactly as you said.
If I recall correctly, the X1300 Pro was in the league on the X700 (non Pro) which was a direct competitor of the 6600 (non GT); the 6600 was faster than the X700 (non Pro).
The X1900XTX is still a great card to have in a Pentium 4 / Athlon system for legacy gaming or even as a secondary machine when needed. You can still game new games at lower resolutions and quality settings with that card. It has similar horsepower to the cards powering the Xbox 360 and PS3. It's from the same generation and time.