ode I believe you are right about the coming wave of high COR faces. In fact, considering the sales appeal of length, I'm surprised it hasn't hit yet.
Cavity backs are usually considered to be more of a game improvement design. They are more forgiving on off-centre strikes and I believe have a higher MOI, which helps keep the club square. The MB is less forgiving on off-centre hits, but as a trade-off, is longer on centre-of-face strikes. They are also easier to "work" if you have a more developed ability to control the face angle.
I was just wondering if Jeff/Hireko actually designed these traits of the MB into this model. That is, is this a true muscleback with their pros and cons that suit a "player," or is is the MB simply the same as the CB design with a back plate on it to make it look like a MB? From what you are experiencing, the two designs are, in fact, be different.