Ron, welcome. You don't mention if you're planning to use a sub. If you are, the M22s plus a good sub(such as the EP500 which I use with my M22s)would be excellent in that size listening room. If not, and you want deeper bass extension, the M60 or M80 would be the better choice. No speaker can overpower a room; you, not it, are in control of the sound level.
The speaker locations you describe sound fine; as long as the rear ports have at least a few inches of "breathing room" they can be close to the wall behind them. The more important factor is to have the center of the woofer cones at unequal distances to the three nearest room surfaces(floor and two walls)so that boundary effects don't pile up at the same frequency.
