I have a ? on 3 blade vs 4 blade props, I currently use a 3 blade 14.25x21 prop for cursing, and I switch to a 3 blade 14.25x19 prop for water sports, I was looking at a 4 blade prop and it says to go 2 lower from your current pitch, so my question is if I run a 21 pitch I should drop down to a...