New prop test results

[McGillicuddy]

I finally ran a new Merc Black Max 13-1/4 x 17 on the Seafari yesterday - closer but not quite there. 2 of us ran with 30 gallons of gas, 20 gallon bait tank, a pretty standard fishing gear load. Got 30 knots from the 115 hp I-6 but only 5000 rpm. I went from 4400 rpm on a 21 pitch to 5000 rpm on a 17" pitch. I was hoping for at least 200 rpm gain per inch of pitch drop... I guess I'll have to drop some more pitch. Gas was old. Would that have any effect on rpm? Also have a stingray foil which I'll shed next week for performance comparison. I'll check my cav plate height, too. I was hoping to get closer to 5500...
Any thoughts?