I flew mine with a SuperTigre GS 40 for awhile . It actually pulled the cub around pretty good with a 11x5 prop. I then installed a Magnum .52 4c with a 12x6. It also pulled the Cub pretty good . But then again , it does`nt take much engine to fly a Cub.
The .70 4c is a perfect fit for this Cub , but an OS .55 would be a good match for it as far as 2 strokes .
IMHO, I think the OS .55 and .75ax have more mid-range power other 2 strokes . I`ve only flown the .55 , and it had a pretty torquie mid range for a 2 stroke.