Not sure BN, and I don't think the current owner has had opportunity yet to find out, as he's only used it on inland waterways, but perhaps around 20 knots. That's only half the potential for the boat with petrol power, of course, but without the noise or fumes. Now, some people may actually find the throaty grumble of a Ford Cosul exactly to their liking, but for the rest, then maybe the stealthy, silent approach may be appealing.
PS Like the new look BN. Can't comment on your relevant posts, though, as they seem to be locked?