That didn't help.
Also, it should be noted that X's CPU usage is very high. As I'm typing this message, it's at 33.6%, and when switching workspaces or moving a window, it hits 99.9%.
EDIT: When I removed the Option NvAGP 0 line from the AGP card's section, while leaving them in the PCI card's sections, it worked much better. Some things are still sluggish, but for the most part performance has been significantly improved. I guess it's not going to get any better than this.