Do you have a tacho on the boat? Before changing the prop, you need to know what it's running at at WOT, based on normal load, and within the maximum operating rpm of your engine (great engine by the way). As a general rule of thumb an increase in 1" pitch will lower the rpm by 200-250.
Avoid the Yammie stainless steel props and stick to aluminium.
I'd also send your existing prop off to be refurbished.