The reason 2 strokes make more power than 4 strokes is that the 2 S is firing every time the piston goes down. The 4 S fires every other time. The general rule in the automotive industry is that 4 S engines make 80% of the power as the same size 2 S engine. However the model engines we use have much less of a gap in my opinion.
4 S engines are a lot more complex and expensive. I am a big fan of both.
Ibelieve the .50 size 4 S engines offered are meant to replace .40 size 2 S engines. Ihave a .52 Magnum 4 S and it makes the power of a 40 plain bearing engine.
I would use the larger of the sizes to replace a .45 size engine like .56 to .61 size 4 S engines.
Ipersonally have had a lot more trouble tuning the idle on my 4 S than any 2 S.