Why is the ARB2 path so slow on NV30? Just the higher precision alone doesn't seem to account for NV30's performance given that it runs at a much higher clock speed versus the R300 and 96-bit vs 128-bit is but a 33% difference.

Apparently, the R300 architecture is a better target for a straightforward assembler / compiler, while the NV30 is twitchy enough to require more serious analysis and scheduling, which is why they expect significant improvements with later drivers.