If me, I'd try the stock 21 pitch to get you more in line with your recommended rpm range. That'll get you more in line with truer needs. Rule of thumb is for each inch if pitch equals 200 rpms,, up or down. That's given you are using a 3 blade as pictured on the boat.

I'd first find some input from the same hull owners as to proper propshaft height and then go from there. If you are too low, rpms will suffer, too high will usually result in too high rpms and poorer handleing/water pressure/ blow out in turns.

I say check your rpm with it loaded with fisherman and gear and fuel cause you will be mostly running that way. that is the fastest fishing boat not race boat, 18ft with a 90hp i ever herd of, so dont mess it up. lol. i would of guessed 42 43 on gps with that big hull.

Beautiful rig, you should enjoy that one. Looks like you can raise the motor a decent bit from what I can see. Its easy to tune with jackplate, raise a half inch and run it and trim it up and make a few turns. If it doesn't blow out turning or when you trim to where you want to be try raising another little bit. Mark jackplate with sharpie when you start and each time. Once you get to height it blows out (cavitates) trimming or turning drop down a 1/4' and this should have you at your most efficient height. Check your rpm's to verify correct prop pitch at this setting, often you will have to go up 2 pitch. Hope this helps.