Regarding cabins of the two, something became apparent around the time they were engineering the X2 demonstrator: I guess because of the space the mast and transmission needs, on an X2 all of the cabin has to be forward of that location. So the SB>1/Defiant-X cannot use as much of it fuselage length as could a conventional helicopter or Tilt-Rotor. This would drive them to a wider cabin.