It is interesting that Great Planes Designer Mike Cross discourages the use of an OS .91 in the instruction manual. Nobody has said that they wished they had used a smaller engine in the .46 and the .60 size. The engine's hovering RPM's can be brought up with a 4" pitch.........same with horizonal speed. The .46's wing area is 900 squares vs the .60's 1,000 +/1 so there is a lot area to support an extra 8 ounces.
Actually the Saito .91 might better than the OS.......