I only noticed that my config was out-of-date after I posted. For most of the time, I was passing NvAGP "2". Still doesn't work. No 'Failed to verify AGP usage' anymore, but I get "NVRM: Failed to get AGP offset" or similar. (Can't easily check ATM)
Appears there were several problems, notably a typo in the kernel was causing AGPGART to fail silently. After getting AGPGART working, though, the Nvidia driver still screws up, with the above 'AGP offset' message spamming through the kernel log. The renderer string, X log, and /proc/driver/nvidia/agp/status all show AGP usage, but glxgears scores are still very, very low, and 3D is buggy/nonfunctional.
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