A little late to the reply on this, and some of my response/info is going to be cut and paste from another post I made.
Bottom line is Darrin at Sensenich is a great resource. Or give whirlwind a call. Both have been super helpful over the years with different airboats and props I have had. A little info on my boat below.
On the dyno my engine came in at 1143 peak TQ at 4300 rpm. 1119 peak HP at 5900 rpm, 93 octane. I told the builder to focus on 5400 rpm as maximum, turning 5 JX blades and a 2.55 box at Darrin’s recommendation over at Sensenich.
My Alaska/Utah boat is prob around 4,000 lbs all in with couple of guys, gear and 50 gallons of gas. It runs dry very well. I have the blades pitched for push not speed at 20 degrees. Max speed is 60 mph at 5,000-5,100 rpm.
When I was having this boat built at the end of 2019, the team at DB was split down the middle on 4 v 5 blade. 4 blades grabbing "cleaner air" v 5 blades and more surface area. Which is where I decided to pick up the phone and call Darrin.
In my reading, more and more boats pushing 4 or 5 blades are using 2.5 or 2.6 reductions v 2.3. So I would also be open to that conversation.
I also found that the sweet spot for (maximum low end push) for my current build is having the props pitched at 15, whereas I initially had them at 20.
PM me if you would like further conversation.