I made it into the Burton flagship store in LA before thanksgiving and according to the guys in the store, the 2013 Cartel highback has enhanced torsional flex but is as stiff and responsive as ever when pushing straight back into it. That combined with the usual level of stiffness in the baseplate is apparently why they still rate the 2013 Cartel stiffer overall than the 2013 Malavita. This is for both Reflex and EST versions.
I ended up getting the 2013 restricted reflex malavitas with the wing highback. Sweet binding and the highback did not feel stiffer than the cartels in any direction to me but this was just in the store and I did not analyze it too closely.