Warped, On your #2 with 91 fx, I have found my favorite prop to be the 15-6 Pro-Zinger. I have tried several but the Pro always seems the best. I love APC props as long as they are under 11". Over that they just seem way too heavy and really slow on throttle response. I have a couple 15-4W APCs I bought for my UCD that I'd be happy to sell cheap if anyone wants them.
basmntdweller

PS at least 14" on the 91FS, 13" isn't enough to give decent vertical. IMHO