I'd agree that bigger blades and less pitch is called for.
Something to keep in mind is that stainless props are more expensive than other options, which creates a double whammy for pontoons. First, because there isn't the same depth of experience in pontoon props that there is in mono-hull props. Second because pontoons tend to be common on very shallow water.
I would offer this suggestion...
Try a relatively low cost aluminum prop in either 14x13p or 14x12p. See how it works for you and whether you need to go up or down. Be aware that going to a stiffer steel prop is like increasing your pitch slightly due to less elastic deformation in the blades. Or at least that's what that engineer guy I spoke with said.
Once you have you "cheap" prop dialed in, if you feel that you're on deep enough water to run a stainless prop (The concern is the blades hitting objects on the bottom), then you can go ahead and buy it. PLUS you now have a spare for that "just in case" situation.