I have the IVO Magnum in
flight adjustable 3 blade prop with 45 to 105 inch pitch range. I
believe it is 68 inches long, but it MAY be 66
inches. I do not think I could go much longer as I would be concerned
about clearance issues with the ground.
Chris;
I have a fixed pitch 3-blade 66” dia,
80 pitch on my 20B; and get static rpm of about 5400 with the 2.17:1 re-drive.
Same specs on different props will give different results, but it would suggest
that you are not getting near full pitch.
Al