35 Donzi ZF prop question
 

My buddy has a 35 Donzi ZF with twin pro max 300's on it. He has 22 four blades on it now and it seems it needs a different set of props. Talked to a guy at mercury and they said 3 blades 20 or 21 pitch. Was wondering if anyone on here has a similar set up and spins a 3 blade 20 or 21 pitch prop and what prop it may be. The motors are not making the max rpm and seem like they should preform better planning up etc. Thanks!