Ericscher, what gear ratio is your F50......1.85 or 2.31 ?
2.33
If you check the performance bulletins offered by Yamaha for pontoons, you'll find that every pontoon tested with an F75 ran a 13 5/8 x 13p prop and turned it @ 5900+ rpms.
In fairness, those are new boats with clean logs.
Of course, you're absolutely correct... the 14x11p COULD work out to be just right.
Using these tests as a reference point, if I were to buy a new Yamaha prop, I'd opt for the 14 x 11p on a Bennington 22 footer.
Well, you really wouldn't be far off with that choice, IF you were off at all.
I bought my boat with the 14x9p mercury prop on it, because that's what the marina owner specified for it, based on his experience.
Not being willing to leave well enough alone, I bought a 14x10p and a 14x11p and tried them out. Currently my motor wears the 14x9p.
Having said that, as you point out next...
The blade shape, area, rake, prop diameter all come into play along with the pitch of any prop. It's always a crap shoot.
I couldn't agree more. But at some point we DO need to make an educated guess anyway.
If there's one thing I've learned in my 20+ years of set-up / driving a race boat, the search for the "perfect" prop never ends.
Of course not. Why give up the FUN part of hot-rodding? 
I've tried many, many different props and engine set-ups on our tritoon to get the performance / speed to where it's at right now. I'm very pleased with what I've accomplished, but never completely satisfied.
I can relate...
You know, for what it's worth, a lot of pontoon owners with big outboards have found that a hydraulic jack plate is a beautiful thing. I've spoken with many guys with 25 foot tritoons and 250hp engines who get over 50mph on GPS.
Just something to try if you're so inclined.
Happy boating...
