I, similarly to Pryso's friend, had Duntech Princesses in a 20 x 18 room with openings going out from the back side so it presented a larger acoustic space, and I think that was the most a room of that size could handle (I tried the Duntech Sovereigns, equivalent of the Dunlavy SC Vs, and felt they were just a little too large for the room). I think the room size you are talking about might be better suited to the SC IV or possibly the V. Part of it is the distance you need to sit back from the speakers for proper driver integration as Pryso notes, the other is bass loading in the room. And I agree with others above, try to avoid a square room if you can, since it is being built. The VIs are a great speaker system, but I think to hear them at their best you might need a slightly larger room or some room equalization to tame the bottom octaves.
