Most AGP cards available for sale these days are 8x. I did manage to find a 64MB 2x card, the Connect 3D Radeon 7000. So it's a toss-up between that, somthing like the PCI NVIDIA GeForce FX 5200 128MB that was suggested, or maybe the PCI 3DFuzion GeForce FX 5500 256MB.
If it helps, let's say...