I am yet to see an X1600XT on AGP which means it would probably be an X1600Pro, these are pretty unpowered, can barely beat out a GeForce 6600GT. The X1600 also isn't a true 12-pipe card as it has only 4 ROPs (if I remember right) which decimates its real performance.
Possible alternatives are:
6800LE/XT (8 pipes but unlocked and it's a monster, 12 pipes beats my X800GTO, 16 pipes and you're laughing)
7600GT (not sure if these come in AGP)
X800GTO (I have one and its quite good)
X800GTO2 (can be unlocked to 16 pipes in some cases but not sure if AGP variants exist)
Don't get suckered in by 512mb RAM, it's a gimmick because the uninformed think, more RAM = faster which isn't true. 256mb is plenty adequate with 128mb usually enough as well.