The 7800GS would beat the X1650 pro in almost every game, it's simply a higher performance card as the X1650 pro is like a 7600GS.
The X1650XT would trade blows with the 7800GS and IMO is the better card of the two at stock speeds. The 7800GS is a nice OC'er though. It just depends on your games. If you plan on putting a few hundred hours into Oblivion, the X1650XT would have been better. And right now cheaper too.