This states that the prolated spheroid has a 15% advantage over a 'bi-hemispherical cylinder' which I assume is a hot dog shape. This is by volume, not frontal area.
My question is why it looks faster backwards. I surmise the area ahead of the propellor acts as an invert Coanda nozzle. Laminar flow all the way to the tail. Maybe a little Meredith Effect?