DonRoc

You cant just go run it WOT and see what happens. what if you have a hyd cam and its propped small, you will over rev it an might drop a valve. Or even a solid lifter motor same thing just a little more RPMs before you smoke it.
You need more information on the motor and cam, then prop to stay below the max RPMs as recommended on the cam card, or get the build sheet hope there is a dyno sheet and you can prop for max HP RPM's.
Talk to the past owner, ask what RPMs the ran. You should not have to experiment unless its a repo and you cant contact the past owner.

GPM

Sorry, I wasn't suggesting run it till it blows, I would hope there's a rev limiter on it and it's set where it needs to be. And maybe the previous owner had it dialed in, and that is the best set up for the boat. People don't always change stickers when they change gears , you could turn the motor over by hand until the prop turns one turn, and calculate your gear ratio. I just thought a little more seat time, wind it up a bit higher, 5500 or so, and see what it does, before you spend a bunch of money possibly for nothing. Good luck, congratulations on the DCB!