You have definitely got something wrong, I have a 21.5 foot boat at 2000 kg dry. Engine is a 1999 5.0 Gi with 600hours on it. However it has a duoprop leg with F4 props..
I can pull 5000RPM and get 46MPH (GPS) down here in the Med.
I can pull 5000RPM and get 46MPH (GPS) down here in the Med.