that's going to be an awesome set-up
Check out the Yamaha performance bulletins and you can find a similar size boat with that motor. I was looking at upgrading to that motor for my boat after my F225 was stolen. Right now my (lightweight) 23CC has a F250 and I run a 19 pitch 4 blade Merc prop. With a 4 blade you can move the engine up a little.
My guess would be you could spin a 21 pitch no problem
I would recommend contacting Ken at prop gods