Try to stay in the 4 or 5" pitch range. You have already found that you needed a wide blade to get the performance you want, and you don't have the available torque in your 91 to turn a 19" prop without putting a huge load on your engine. I don't care how you look at it, yout rpm will go waaayy down with an 18 or 19" prop. You will think that you are trying to fly scale.

The Zinger Pro props are ridiculously inefficient, well below the performance of the Zinger standards. The MSC props give a lot of thrust not found in Zingers at low rpm, and have a "predictable" feel as the rpm increases. The blases on an MSC wood props are wide all the way to the hub. Carbon props are really heavy, are hard on the engine if a blade strikes the ground, are expensive, and are don't give as great a return to the smaller engines as they do to larger gassers.

Keeping the prop light reduces the engines "spool up" time. something you want for 3D. I would stay with the wood props, and do some experimenting. You may already have the best you can get for your plane and engine combination, but I don't believe so.

Just my opinions.