Max prop on a saildrive
Your MaxProp, for that matter almost any 3 blade feathering or folding prop, will deliver much better than 75% efficiency in forward (compared to an equivalent sized 3 blade fixed prop). The advantage of the Max is that it rotates its blades in reverse to turn its blade leading edges the most effective orientation for reverse. This actually increases its backing efficiency as much as 80% over that of a fixed prop. See this URL for the particulars.