if you are looking for good speed with 150hp, your 17pitch should do just fine. anything steeper than that wouldnt do you any good(the old hp vs. wieght vs. drag ratio thing). plus, with an 18 or 19pitch you would be burning a crapload of extra fuel coming out of the hole. unless you go 225hp or more a big pitch prop isnt really gonna do anything but burn more fuel. :'(