The Magico M3 would, without a doubt be a perfect speaker for your room. Your room is large enough to handle most all size speakers without a port. The M3 bass extension is only in the upper thirties. This would be sufficient, but going into the low 20’s with bass extension would enhance things. To me, the M3 is a end game speaker.
They mate perfect too with my REL friends, if you feel you want full range. I’m so glad that your room is the proper size for achieving the pinnacle of sound systems.
I listen 9’ away, and Montis is 6’ apart center to center, and 3’ from the back wall . Montis is slightly toed in, but not as much as the Martin Logan flashlight test. Having the Montis separated at only 6’ from each other dilutes the few degrees more toe-in that is recommended. I have a soft chair centered, that is a clone of the Maxell Man Chair of the ads years ago. Just made of cloth though. Finishing touches is (3) blue aquarium lights placed low for effect on the back wall (Stone Fireplace). Took me about 9 months and a whole lot of amplifiers and cables to get everything up to the standards that I have.
It makes me wonder about how much better that ML 15a would sound in my room, with the Anthem Room Correction. I’m at "WOW" with the Montis and RELs now. I also have 2 more REL S3s sitting in a box, but I have decided that just 2 RELs is plenty. REL S3s, having a 10" front firing driver and a 12" carbon fiber passive radiator shooting downward creates the volume of a 15" woofer when needed. And it makes for perfect symmetry at all sound levels, even low listening sessions. A few years from now, I can see a yearning for a used set of 15a Martin Logans. Happy travels. I see you taking the right path to sonic freedom and euphoria.