You can always tune for max effect on any given two-stroke w/wo valve but with a valve you can get both bottom and topeffect, but with big volume and tuned for maxeffect a bit lower you loose some top but get a good bottom anyway.
To benifit from exhaustvalves you might have to build a smaller engine and tune for topeffect at a higer rev. and use the port to get the bottom, or rebuild the big engine to allow it to rev higher witout "expolde" to get more top.
You get a broader register from moving the top higher witout loosing the bottom or more bottom witout changing the top.
Question is if we need it on a boat, fueleconomy perhaps but 150hp is 150hp if you use it...