It's not the size of the airplane that should determine your purchase, but the features of the system. You can fly any size airplane with the Futaba 8J transmitter and the receivers available for it. Check the features. For many, the 8J will have the features they desire for the type of flying they do. For others, the 8FG Super's programming offers the options they need.
You can compare the features here:
http://www.futaba-rc.com/systems/feature-compare.html