Not relating to the 91 engine, but to the "w" prop you mentioned. Just for a comparison, I just tried a "w" prop and here is what the rpm relationship was in case you want to judge which props you're trying to compare.

With my Saito .72, I was running a 13x6 at about 9800-10100 and when I went to the 14x4W it gave me about the same but closer to the lower end. That "w" affected it quite a bit considering "in theory" the 13x6 would produce similar results to a 14x5 which would conclude that a 14x4 would then have higher rpms but it didn't so the "w" comes close to consuming the same rpms as one jump in diameter or pitch.

Thought this may help you judge the 14x6W you are seeking and how it relates to your current prop. I found my "w" at Horizon but didn't see the size you're after.

-shaun