The major difference in a 2 cycle Vs. a 4 Cycle on these planes is low end power.
A 2 cycle will do fine for hovering and flying around but their power comes from RPM's. Meaning that you need to be running them in the mid to upper part of their power band to develop the power needed.
A 4 cycle on the other hand puts out a lot more power through out its whole power band. Also, you can run a much larger prop on a 4 cycle wich also meand more air over the tail. That is what you want for 3D.

Dont get me wrong, you can 3D them with a 2 cycle. Its just easier and more efficient with a 4 cycle.