Make sure the X700 is AGP assuming that is what you need. It is a plain X700 not a PRO, that is why it is priced near the others.
OK, honestly, I don't like your choices and would wonder what a 9700 pro, 9800 pro, 6600GT, and 6800le would cost. All much better cards. But of your choices, I'd say the X700 would beat out the others by a little in almost any game. The 9600XT is about equal to the rare 256-bit 9800se and ahead of the more common 128-bit 9800se. So forget the 9800se (*sorry Wusy*).
<A HREF="http://www.digit-life.com/articles2/digest3d/index0507.html" target="_new">This July Digest from Digitlife</A> shows how the 9600XT and X700 compare to other cards. In part 4, click the games and resolutions that are important to you. You'll see the X700 probably beating the 9600XT, but also see other cards blowing both away. Before buying you may want to check out the prices the faster cards I mentioned above.
<A HREF="http://service.futuremark.com/compare?3dm05=658042" target="_new">3DMark05</A> <A HREF="http://service.futuremark.com/compare?2k3=3781954" target="_new">3DMark03</A>