In that size room, I too(of course)recommend the M3s. Not only are they a bit more full-range but having five of them will make for near perfect tonal balance from speaker to speaker pans. Also in that sized room, a sub may not be needed with M3s for those times when quiet must be maintained in the rest of the house.

Only problem I can think of is they'd be a little harder to hide in the room than the M2s.