Update - I have a tach now and with a "normal" load I am running 19mph at 4300 RPM
I have a 15 foot fiberglass deep semi-V hull with a LOT of plywood which equals a lot of weight.
The hull was originally bare, but has about 3 sheets of 3/4" plywood for decks, 3-4 eight foot treated 2x6s, light carpeting, 12 gallon gas tank, 40# trolling motor, outboard/steering console, 40 lbs of tackle, etc...
My 1977 40hp Mercury has a 13 degree aluminum prop and with me and my daughter it will run 20 mph on the GPS. Add my wife and my other daughter... 18mph, and last night I added a friend and his camera equipment (fireworks pics) - about another 350-400 lbs, and 13.5 mph was tops.
I don't think I have any trouble with my "holeshot" but it makes sense to me to drop down in pitch to get RPMs up.... but the boat does seem to take off well, even very heavily loaded. So maybe I am confused and should go with more pitch...
I do not have a tach... sorry for lack of info. Is there an obvious direction to go here?