Yes, those Avengers look good too. I think a "48 inch foamy class" for 15 power would be easy to build. Set the max weight at about 30 ozs and have NO minimum weight. Use birch dowels for spars and build them similar to the AMA C/L Combat planes that were / are all foam.

This is basically what I fly combat with around here, retired C/L Combat planes that I put a pair of tip fins and elevons on, and fly with .15s. The engine mount is little aluminum beams that stay with the engine and get clamped to the center rib of each model with a single bolt...so no individual mounts need to be made for each plane.

If everyone is flying 48 inchers, you level the playing field. 48 inches is a handy length for materials.