[tsubaki]

The one I have is for a different purpose than what you are intending to use it for.
I'm primarily using it for shallow water and to raise the motor when stored trailered to have the motor vertical and for the boat to drain.
The idea as far as better performance in rough seas should pertain to smaller boats that tend to wave skip causing cavitation (ventilation), the larger size boats may not have that problem.
An untested portion (as far as I know) is what my neighbor has. His 21" prop ventilates when starting off (it takes several careful seconds to get on plane) but will run 45mph. The 17" prop immediately gets on plane and carries any load but only does 37mph. The thought process was to use the 21" prop, install a jack plate and run deeper till getting on plane. So far he ain't spent the money on one to try it.