I wish I had a simple answer to that good question. Chapter 7 in the 3rd edition discusses the audibility of early lateral and vertical reflections for several different sounds - and it makes a difference. I will try and find some rational comments when I finish examining the page proofs of the 4th edition, which discusses the topic as well, and then compile a useful index - a difficult job. Business first
Off the top of my head, I would estimate that there is little experimental evidence to support advantages to either large or small rooms above the transition frequency. But having lived with both, I favour a large room in part to be able to get farther from the loudspeakers (the musical instruments). That said, we need to get specific about the dimensions at which there is a transition from small to large. Good luck with that.