I would just like to add one more variable to consider. And that is the airframe the prop is being used on. If the airframe is very sleek and slippery, you can use more pitch than if the airframe is blunt and draggy. For example, my Kougar , which was fairly slippery used a 10X8 prop on a OS 50. It might have been able to handle a 10X9. I would never try to use that much pitch on a dirtier airplane. Again, this was for top end speed and meant giving up some climb performance. But with enough speed, who cares or notices.