8 to 9 feet is very sweet. You won't have any issues with multiple drivers from an M2, M3, or M5 fusing at that distance.
Don't think you have enough info to say that Mojo ... need the ceiling height, the listening area width, and if he's going for Atmos only or if Auro is in the mix ... and that's at a minimum.
As far as an M3 or M2 (don't know if you want to hang an M5 on the ceiling and distance to listener would be a bigger factor). I think both are matched well enough. The M3 will sound slightly deeper then the M2 but your giving up some clarity in the mid range. I went with M3's as I felt that one would not notice the difference as a surround is not something you're going to be doing critical listening with. Both are damn good even as mains when a sub is in the mix. Perhaps my ears are not good enough anymore as I only hear the difference when listening for what I know from side by side testing (Mojo probably has a better ear and sonic memory).
I can not speak to Trever's concentric lobe stuff ... as I've never noticed it in real life. So, You know my take ... it's MHO and your milage my vary.
