As it turns out, I did just that (again.) I'm not sure what I did differently this time around but "NvAGP 1" successfully enabled AGP at 8X with SBA. Fastwrites appear to be unsupported with this chipset even though lspci -vv on the 645 seems to indicate it could be turned on. I'll have to twiddle with it and see what happens. The only real issue I have now is "screen jerks" even when doing non-OpenGL things like reading email. I believe this is due to my using the experimental Render feature. If it gets too annoying I'll turn it off.