I have a room that is 12' square with a window on one wall, a door opposite that, and two of the walls have angles to the upper 1/4 of them. All the walls and ceiling are horsehair plaster with 30" of blown in insulation above and 2-1/2 foam insulation on the walls with the angles. (It's a third floor room, roofline intrudes.) On the floor is 1/2" pad, thick plush carpeting over that, and a Berber rug over much of that.
I've tried two different floorstanders in the room, and did live with KEF LS50's in there for about a year. The floorstanders were overwhelming for the space. Now I'm running KEF Reference 1 speakers and they're the perfect fit for the room.