That room is perfect sized for the Arcs. The Arcs sound different because of the steel and carbon fiber cabinet - they disappear so easily, but for some people they disappear too easily. You lose that slight coloration that comes from wooden cabinets.
To a lot of listeners, that coloration warms the sound, which they like. I think this is why you'll often hear people describe speakers like YG, Wilson Benesch, Magico, and others that use metal cabinets as "clinical" or "analytical" because the speakers are a little too transparent for them. It may sound counter-intuitive, but not everybody wants to hear exactly what is on the recording, especially if it's a mediocre or bad recording.
My reaction was overwhelmingly positive - I liked the sound so much, and the effect of removing the wooden box from the sound, that I went and bought more speakers with non-wooden cabinets (the PureVox). I want my speakers to completely disappear in the room, I don't want to hear any coloration. It's true - bad recordings sound bad on the Arcs, they don't mask anything and they don't "help" bad recordings, but good recordings sound wonderful.
The difference between the Arcs and the PM1 - which you do have access to for reference - is huge. I've done this comparison in my home, and at a dealer, with the same result. PM1 sounded like it had a wet blanket thrown over it. You just have to decide what sound you want - the transparency of the Arcs is amazing if transparency is what you're after.