I haven't flown both just the magic extra but i have looked at both and here's what i noticed.
1) simply magic has the cowl, looks nicer adds weight
2) the fuse aft of the canopy is somewhat thinner on the simply magic
3) the tail surface on the simply magic is shaped a bit different and the rudder area is some what smaller not good IMHO
4) the landing gear is stright and it looks a bit shorter/lower to the ground on the simply magic also not good IMHO
5) the wing on the simply magic has 30 more sq inches of area,not enough to make any difference

there maybe some other differences, these are all I noticed. even though i haven't flown the simply magic i really don't think it will fly any better than the magic extra, as a matter of fact i think it would fly a bit worse for the 3d stuff due to the smaller tail surface area and extra half pound or so in weight. the magic extra is a real nice flying plane and does 3D ok, if thats what your after get the magic extra.