If a cub is stalling at 23 mph, how on earth would you be able to slow it down enough to land without it first falling out of the sky? I'm not sure about all this analysis, but most cubs I've seen can slow down way under 23 mph and keep on trucking. I'd say prop an engine to get it within it's useable power band, and the style of flying you will be doing. Generalizing prop numbers for any given airframe is just guess work. There are far too many variables involved, like drag coefficients, Reynolds numbers, prop manufacturer, density altitude, etc.

Jesse