if you were at 4600 would expect dropping 2" and adding a blade would get you around 4800-4900 or so at WOT.
Just did a similar swap on neighbors 20-21 ft Larson with a 4.3 Volvo MPI, had a 3 blade 19" Aluminum VP prop and was low on wot maybe 4400 or so, went to a 17" 4 blade VP prop hits...