Go with the 4 stroke if you really want to have fun with this plane, you may want to look at a couple of weights though, the OS max 70 surpass II weighs 22.4 OZ and has made it difficult to get it balanced for 3-D, I had to cut a pop hatch in mine behind the wing, but that motor is POWERFUL, and with the new pop hatch and the battery back there I am right where I want to be.

The Saito .82 seems to be the choice for other users, and I haven't heard them complaining about CG weight problems, But I'm not familiar with the saito line yet, I have never owned one, I veered from OS max once and was very disappointed, So I am A hooked OS max Man myself, that engine has taken more abuse including being under water in a pond, smashing into cement,asphalt,mud,grass, buildings, at high speed. and just keeps ticking great, I'm almost afraid to spend my cash on another name, even though I've seen the other engines working and they all seem to be pretty good.