Some of the very best sound I've heard involved large systems playing in very large rooms. One setup was a dedicated listening room that was about 27' x 50' x 12' or so (just guessing) with a massive horn-based system. The other was a system using three Wilson MAXX 2s and two WP-7 in a pretty large conference room (at CES). I have also been impressed by a quite small system (YG Carmel) playing in a quite large ballroom. The space helps very much in giving the presentation proper scale. Wide spacing of the speakers also makes it possible for more than one person to be located in a sweet spot (in almost all typical home setups, the sweet spot is really far less than one foot wide).
With something like a Maggie 20.7, there might be some restriction on size if one wants to listen at high volume because of the amount of power that would be needed and the possible limitations on the speaker delivering high level of bass. But, I bet that at reasonable levels, Maggies would sound great in a large room (I have only heard them in a room of about 16' x 25'). Just a guess, but your hypothetical big room would not be too large and would be great for delivering realistic size to the soundstage.
With something like a Maggie 20.7, there might be some restriction on size if one wants to listen at high volume because of the amount of power that would be needed and the possible limitations on the speaker delivering high level of bass. But, I bet that at reasonable levels, Maggies would sound great in a large room (I have only heard them in a room of about 16' x 25'). Just a guess, but your hypothetical big room would not be too large and would be great for delivering realistic size to the soundstage.