I've got two standard rotation 04 150 carbed yamahas behind a 24' Grady White with a full transom and bracket. It's a walkaround model with a hardtop. Without gas and gear she's a good 4,300 lbs. Throw in 90 gallons of gas, wife, kids, dog and a months worth of towels, food and suntan lotion (might as well load the entire house contents) and she's pushing 6,000 lbs. I've been told to start at 14 x 17 and go from there. Should i aim for max rpm or a shade higher? Thanks for your help. 