OK so I didn't see any major issues with this version, on my 550mhz machine this is pretty much constantly stuck at 60fps which is what you would expect. I also didn't notice any significant bottlenecks related to action happening on screen. Input delay is not back to an acceptable level and fine to play with.
I don't know how far you want to go down the optimisation route - I can artificially reduce down to 200mhz natively and intentionally bottleneck the CPU to understand the relationship between the 3dfx renderer and CPU load. At 550Mhz there is enough CPU power to calculate the game logic and handover to the graphics card at 60fps continuously.
When moving down to 200Mhz, there is a non-linear benefit between the software and 3DFX renderer. When graphics load is high, there is a +82% benefit, when graphics load is low there is a -45% benefit. That may indicate that geometry setup and GPU management is taking a significant amount of CPU time.
Alternatively, it may mean that the voodoo3 card can't take advantage of dirty rendering like the software version does and has to re-render the entire screen every frame even when the viewport size is reduced. But I don't think it's that because a similar effect is observed between 640x480 and 800x600, where the software renderer gains 50% and the 3DFX renderer only gains 12% even though both are full screen. Plus the voodoo 3 has plenty of fill rate anyway.
At 800x600, the 3DFX renderer at 200Mhz has about the same performance as the software renderer at 550Mhz. So at least you can say there is a significant benefit at high resolutions. It's not a constant 60fps but it keeps you in the 30-60 range. I was also thinking, the geometry setup probably requires FPU and pentium CPUs will overperform there compared to K6, Cyrix and 5x86 class CPUs.
Note: This is standing on the cinema bathroom stalls looking towards the mirror in hollywood holocaust, it's a heavy render for the engine
98/DOS Rig: BabyAT AladdinV, K6-2+/550, V3 2000, 128MB PC100, 20GB HDD, 128GB SD2IDE, SB Live!, SB16-SCSI, PicoGUS, WP32 McCake, iNFRA CD, ZIP100
XP Rig: Lian Li PC-10 ATX, Gigabyte X38-DQ6, Core2Duo E6850, ATi HD5870, 2GB DDR2, 2TB HDD, X-Fi XtremeGamer