Hi
On our boat a 5.3m Humber with a 90Hp 2 Stroke outboard. Aging Youth uses a 19inch S/S Laser II when trimmed right out and at WOT setting we maxed out at 5800rpm and 40knots recorded on the GPS. Just Ask Whiteshoes
who was parallel with us on the last littlehampton cruise.
I know Mike C is hasving the same problem with prop selection and it is a lot of trial and error if you can afford it.
Good Luck.