Sure the M80 will be fine. It will produce sound, with more SPL than you can handle. But I still maintain the 60 or 660 will sound better. They are apt to deliver more linear bass and acoustically disappear better.

The long wall is usually discouraged for bass reasons. My living room, same size as yours, is set up on the long wall and I love it although bass was a real challenge. The 60 and 660 would be great in that department. Expect a hugely wide and enveloping sound stage on the long wall and awesome mid-bass, particularly with the 660, even at low volumes.

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What I can't tell you is if the 60 or 660 would disappear as well on the long wall. My M100s, active LFRs and M80s could not. The M50 and M5 bookshelf were better. The M2 bookshelf and OW completely disappeared and so do the M5OW. I give a slight edge to the M2OW actually.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated