The M22 is a great speaker and I enjoy mine greatly, but the reason it is more expensive that the M3 is that is produces such a clean and nice mid-range. Because of the height that you are having to mount your speakers, the perceivable difference between the cheaper M3 and the M22 would be much harder to notice so honestly I wouldn't spend the extra cash. The M3's will also not be as tall on the wall mounted stands. (And as a side note, the M22 is a 17 pound speaker so wall mounting brackets would have to be very strong and secured properly to a stud)
