Re: 2 2x12 vs 4x12 cab?
I think it all depends on the space where those speakers should kick the air.
When in a limited and closed space, the kick of a 4x12" can be too much, specially with powerfull amps. Basses can resonate with a mode of the room, booming the middle-lows and confussing the sound.
For this applications, a single 1x12" with good projection and 3D representation is good enough but, sure, a 2x12" is a good enhancement and not so excesive as a 4x12".
For wider and opener spaces, a 4x12" (at least) is what you need to push the air.
If your speaker would be miked then, just go with whatever it works well for you (sound-wise and ergonomic-wise).