Who's the best to consult on prop selection? I'm not satisfied with the performance I'm currently getting and want to make some changes.
Go right to Ranger. They do (or used to) quite a bit of prop testing with all of their hulls.
is it a 21 pitch 3 blade prop? if so, i personally would stay with a 21p but go to a 4 blade or even a 5 blade.. i run a 5 blade on my 200 merc on the back of my fx18dv and love it. but that being said, my boat is not a ranger so results will most likely vary. if you know anyone that has a 4 or 5 blader ask them if you can try.
Yamaha has selection guides for specific boats right on their site to get you close anyhow.
I looked over at Yamaha and you are right on @ 21P but diameter is what makes and breaks just as much and you didn't supply that. Another thing is every brand is a bit different, they all have different cup angles ect, I like Yamaha props the best, I have tried a few different ones on My F150 on my pontoon and Yamaha props perform the best.
Also what engine mount height hole the engine is mounted in can make a big difference too, on plane the fin on the lower unit should be right at or about an inch below the water line for quick reference.
Here you go.
http://yamahaoutboards.com/owner-resources/performance-bulletins