Don't get overly hung up on slip.
The stamped pitch vs actual pitch of the prop can vary considerably, which messes up your calculations.
Everything else being equal, lower slip is more efficient, but everything else is never equal, because to reduce slip you've usually had to compromise on something else. e.g changing from a 3 to 4 blade prop of identical blade shape should reduce slip, but might also reduce top speed because of the losses from the extra blade.
FWIW, always go with the smallest possible blade area, and min no of blades if you want max speed - the compromise in this instance likely to be planing/low end pull, which for a "lugger" may not be desirable!
If anyone ever claims to be a prop guru, ignore em and ask someone else. It really is an art on anything hi-performance.