There will be a big difference in efficiency between a reasonably good mechanical variable speed transmission and an electrical "pseudo transmission".
Electric motors run at their most efficient at fairly high speed and tend to be less efficient at very low speeds. Any electrical speed switching or limits in a controller can't overcome that. A mechanical variable ratio transmission will allow the motor to work in its efficient speed range even when the wheels are turning at low speeds.
Jeremy
PS: BTW, relative to your PM, I don't know of any motorcycles that use dérailleur type gears.
