I put the os91 in this bird and it flys great. I'm using a 14/8 prop.
It almost has unlimited vertical. It will climb streight up at least 100 feet or more before it stalls. I'm still experimenting with props. One thing I found out. Don't ever use the thin small ID tubeing in the fuel tank kit for fuel pic up. This was causing my engine to overheat because the ID of the tubing is small enough to limit fuel flow. I just changed it to larger ID tubing and hope for better performance. other than that, it's a nice kit. The tail feathers are full semetrical instead of just flat. I think the airplane performs better with that idea. I think you'll like it.

Good luck.