Most people that I know that fly caps ( Both sport and IMAC) say the Extra is a much more stable plane. The Caps have a tendency to snap when you slow them down. They are better at 3D than an Extra. THe Extra is better at precision flying.
MY recommendation would be the GP Extra or The Wold Models Extra with a ZDZ 50 or equivalent.
I have the WM Extra with the ZDZ. I have heard both planes fly good.