I have both Height and Width speakers and now almost exclusively use only the Width speakers. Based on several factors I think you will also, even more than me, benefit from Width over Height speakers.
First is the size and shape of your room. You have a low ceiling (mine is vaulted so I get more ambiance from the Height speakers than you will and I still prefer the Width speakers). Your room is both long and wide making it more likely Width speakers will spread out the front soundstage giving you an even more immersive 360 degree soundstage. I’ve tried both M2s and M22s as Width speakers for my 3 M80s and found no difference so the less expensive M2s, especially compared to the QS8s will work just fine and because of their small size they are easy to wall mount if you don’t want to clutter up your floor.
If you did choose to use Height speakers your low ceiling would almost necessitate a QS8 type speaker to sufficiently spread out the sound. Also Width speakers come into play in almost every scene whereas the Height speakers only produce sound when ambiance (things like rain, wind, echoes, some music) are playing in the mains.
