When we got the Tom Senior light vertical, the first thing I did was to convert it from MT2 to R8, not only to have much more rigitity, but to share the tooling with the other mill. The original motor was 1/2hp single phase 1440rpm and I bought a Schneider 750W inverter and a 6 pole three phase 1hp motor. The motor runs at 900rpm at 50Hz and the inverter is programmed to run it from 25 to 75Hz. At 25Hz the power is halved and full use of the four speed original belt drive is an asset. I have never felt the need to extend the frequency range so far. Some people do not like the bother of manually changing speeds, but the power stays constant if you do.

There is a Bridgeport style mill on the market with R8 which uses a 5hp motor and needs it at lower speeds as they have done away with the mechanical gear variation. Total OTT for R8 high speeds though.

Running at low speeds is often used when drilling large holes, so low power and torque is not an asset.