I don't have any particular experience with the cub s+ but I will say that changing the prop size from a 9 inch to 10 inch doesn't normally have a huge difference in flying characteristics on most planes. If the prop was included with the floats then Its probably best to use the 10 inch prop at least when you have the floats on. Either way It probably won't hurt to try the 10 inch prop on the cub s+