First off, VF2 will never be emulated with polygons. Model 2 and 2A games cannot be emulated with 3D - 2B and 2C can. See system16.com for which games are which.

The current emulation is missing 2 high-speed DSPs and the entire 3D pipeline. I expect 6-8 GHz to be required for full speed, just as was quoted below.