For the Norvel .061, a lightweight, un-flapped stunter could be as large as 275 sq in. Lee Strickland has had great success with his Ringmaster 250 (sq.in). Keep the weight under 10 ounces dry.
If you go flaps, I would keep it under 240 square inches. The Baby Pathfinder at 235 sq.in. is a great flying plane with the Norvel. The weight better be under 14 ounces for acceptable performance, and I have seen one at 11 ounces that flew superbly.
My own Sky Sport is 180 sq.in., 8.5 ounces and is way overpowered with the .061 (but it punches through any kind of wind!)