There's only one 7600GT card. If you can FIND it (it's out of stock most of the time) it's a damn good card. It is, however, much more expensive than the GS card. This is because there's only 1 in AGP. There are dozens in PCIe.
If you just want to stick with AGP a while longer, skychimp is selling an ATI x800 on these forums. He's throwing in a 1GB stick of PC3200 with it (and asking about $200 for the package).
If you want to go with the 7600GS, it's a decent card. The GT is a lot better. The GT ranks right up there in performance with the 7800GS (probably THE best AGP card in the world right now). The 7600GS will probably run AH just fine. The major difference between the GS/GT is the clock speeds (it does the same, it just does it a lot faster).