Before jumping into an empty pool guessing the right prop pitch, how about placing a Tiny Tach induction tacho, go for a wot spin with current load and compare your achieved readings to factory engine parameters. Then you will know for sure if under or over propped. Is your engine a disguissed Yam or Tohatsu model ?
A good prop selection, the one that will give slight passing midle rpm readings, good hole shot, with good top speed. If engine runs between 5 to 6K at wot, 5.5K or slight passing would be ideal. You could have 2 props, the factory standard and family oriented as spare. Inflate well that sib's tubes, a must have to perform much bettter or as expected.