RE: 1 ring VS 2 ring engines
I think single ring pistons would be an advantage over dual rings in our airplanes because the prop puts a constant load on the engines. With a constant load the vapors will build up between the rings and form carbon deposits more rapidly than most other uses 2 cycle engines experience.
That said if all out performance is wanted it's my opinion a dual ringed piston will have better compression, leading to more consistent power. And more power.