Hi Tengee,
My Pacific Trawler 40, hull #37, is equipped with the John Deere 6076AFM30, specified by John Deere at 300 hp at 2400 RPM. Interesting that they were probably delivered within months of each other, but with different engines from JD??? Although I haven't weighed my boat, I do not doubt it weighs within a few hundred pounds of yours, as mine also includes 65 gal of water and 65 gal of fuel in the swim step.
My transmission is a Twin-Disc, with a ratio of 2:1. Interesting that yours is 2.45:1, which complicates things a bit. In addition, mine is specified at 2400 WOT at no-load, versus your 2600. Some performance results of MY hull, which carries a 25" x 23" five-blade prop, are as follows:
1200 RPM=7.1 knots
1600=9
1800=9.3
2000=10
2200=11
2400=11.8
In my personal opinion, propellor calculators cannot be expected to provide an exact match to hull/engine combinations. They simply get you in the ballpark. Your existing propellor is close, but (again, in my opinion) apears to be over-pitched. As reducing propellor diameter is a one-way street, it would be my suggestion to de-pitch your prop two inches, and try again.
Yes, you can live with an over-pitched prop. Many operators do so, but you run the risk of overfueling the engine at WOT, and having to explain to your next owner (and providing some cash at sale to correct the situation) why the engine will not achieve WOT of 2600 RPM. And yes, anything over about 7.5 knots is in excess of hull speed on our hulls, but so what? For what it's worth, my fuel burn at 1600 RPM is 4.2 gph. That's low enough for me. Still gives my about 800 nm range, not including reserve.
Hope you enjoy your new boat. Mine's a peach.
Regards,
Pete