This is no true..
the carbon version is more and more reactive board...it's like an elastic...nervus..you put forse and the board give the force back...this is the differnce the reactivity of the board...
The weight also...the carbon version is lighter..
For the size...i'm 73/77kg last year i rode with the 133 this year i take the 138, because has different shape an i would use it also with the binding..
But nowaday if you are invlolved in freestyle the 138 is perfect, for freeride, also with 135 antd 75 is perfect.
The board is not stiff!!! is perfect
The Alby Carbon model is Stiffer than the standard one..
Thats about the only difference imho..