The right room.

Based on my limited experience, I'd prefer a room size of about 14ft wide x 23ft. deep X 10 ft high ceiling for medium to large floorstanding speakers placed far out from the back short wall.

These dimensions should suffice for perhaps all but the largest of speakers providing a deep, wide, and tall soundstage with proper speaker placement.

And with a room of these dimensions there should be enough space to play with speaker placement and listening chair placement to minimize most any low frequency suckouts and overloads.

-IMO

From my experience, Stehno's suggestion is accurate.

All room dimension rules are made to be broken but going with a long rectangle as he suggests will give your speakers room to breath and allow them to reproduce even the deepest bass passages.

Yeaaaaaaaaaaaaa my room is 14X23 but sadly I have low drop deiling in basement (7ft) but I run speakers with very little Vertical dispersion. If I had a choice I would extend room size to more like 17X26 or so with a high ceiling. My point of view on room size is for dual use to allow for a larger Projection screen then I can fit now.