Dweller,
I used them in an 11 x 13.5 ft room with plaster walls, hardwood floor w/ thick carpet & pad. Drove them with a Plinius SA50MKIII and an EAR 890 70 wt tube amp (which is not thick or tubey sounding in any way). Music was tonally very realistic but was not as free flowing and open as I like it. And this from a guy who had ProAc 2.5s for 7 years. Things were just a little bland and I would often nearly fall asleep while listening. I kept having to "lean" into the music to find the things I wanted. Drums were especially frustrating as they lacked resonance and impact (kinda like 90% of rock drums recorded since the mid '70s). I found the top end a little lacking and used Tonian super tweeters which helped a lot. all of these things caused me to hear the speakers as being a little thick sounding overall.
By the way, I had a phone conversation with Alan Shaw who told me both my amps were easily sufficient in power to drive the speakers, especially in my small room.
I replaced them with 1/2 the cost Dynaudio Focus 110s and am happy as a clam. I do use a REL sub and still use the Tonians but have them "tuned down" a bit from what I used with the Harbeths. Am now looking for a pair of Focus 140s.
I think it's a bit odd that all the things the new C7-3s are supposed to do better than the C7-2s are the exact things I was unhappy with.