2 big differences. A 4 stroke runs just fine inverted while a 2 stroke just doesn't like it. Even though the 4 stroke muffler is tiny compared to a 2 stroke the 4 stroke engine is much quieter. The biggest reason I see to get one is that a lot of sport planes have cowls that don't allow for the big 2 stroke mufflers and look ugly as heck if you do manage to carve enough matewrial out to make it work. 4 strokes have very small mufflers which are easier to adjust for. For example the Great Planes Ryan STA 1.20 ARF has a shape that is very poor for a top mounted 2 stroke engine. An inverted engine fits much better but doesn't work very well on 2 strokes. The 4 stroke will fit in inverted and the small muffler is easy to make room for.