RE: Katana 46 propeller size?
I'm just about to complete a Katana myself with the OS50SX, and I'm planning to use the APC 12,25x3,75 Wide.
Great prop on 46-50 high rpm-engines.
Edit: ...that's if you like 3D and vertical climbs. If you like more sports and high-speed flying: APC 11x7, Robbe 12x5, or similar sizes.