Horn Speaker Recommendations

Given your budget, you should consider going to New Jersey (Charney) or the Washington DC area (Deja Vu) to get a good audition.  The other choice would be to attend a show that has some of the brands you are interested in.  Although shows often don't present speakers at their best, they at least will give you more than any description or review can ever deliver.  

Although they are not horn speakers, Voxativ makes systems that have similar characteristics--dynamic, vivid, good at lower volume levels.  Another brand (also not horns) to look into is Trenner and Friedl.  Someone, above mentioned Rethm speakers; I heard their $3,000 model (Bhaava) a couple of years ago and they were quite impressive.  The  Rethm had the liveliness of full range speakers (they use a full range driver plus a powered subwoofer), but none of the excessive peakiness that is common to full range systems).  The Rethm was like a bargain Charney in sound quality.   

Avantgarde !

@willgolf  The Classic Audio Loudspeakers model T-3 or T-1 is something at which you might want to take a look.
They are hybrid- using 15" woofers in a bass reflex cabinet, going down to 20Hz. The mids and highs are horns; overall the speaker is 98dB 1 watt/1 meter and 16 ohms. I've used them in rooms about 3 times your size (a ballroom at RMAF) and they produced a very expansive and precise sound stage. We had a lot of fun playing Roger Water's 'Amused to Death'; the sounds from the side like the carriage were spooky!
What's nice about this speaker is the first breakup occurs at about 35KHz, so its very smooth. Due to its field coil operation, its also as fast as any ESL; the result is a very cohesive, detailed and relaxed presentation. In that room we had 140 watts/channel (our MA-1 OTLs) and pretty much had unlimited power. Since they go to 20Hz, no need for a sub or subwoofer crossover- one amp can handle the speaker full range so no integration issues. The speaker is easy to set up in most rooms; I've operated them for years with only a few inches behind the speaker to the wall and yet gotten a very convincing sound stage. This of course is one of the advantages of the controlled radiation pattern of a horn. 

You can find plenty of images on them on line. I've shown at shows with CAL a lot and we've gotten plenty of accolades (Best Sound at Show, that sort of thing) from many publications.

At home my room is not nearly the size of the one you have planned; I use our little S-30 OTL and it shakes the house when the really deep bass notes show up. Yet its easy to listen to all day and can play delicate material with the same ease as bombastic stuff. I've not found a recording that has shown a weakness in the speaker- its good with everything I throw at it.

I did go to Deja Vu in San Diego and I had an extensive listening session with them.  I also have been to shows in New York and LA.  I just got back from a week in LA and San Diego with the sole purpose of listening to speakers.  I am going to Dallas and Florida in the near future to do the same.  My wife does not like the look of Charney and Deja Vu.  If I decide not to go with Horn speakers I am considering Evolution Acoustic Maestoso which is not out yet but I heard a demo of while I was in LA last week. By the way, I love all of the feedback I am getting on my search.  This is a big change as I am moving out of Sonus Faber Amati Tradition Homage speakers, which are fantastic in their own right.

kosst...the speakers would be at the base of the long wall.  My room now is 25 x 40 and I sit 15 feet away and the sound is still incredible.  I don’t doubt that the Duo’s would sound better but I am not sure in my room I could hear $10k difference.  
Rodman... why Avantgarde?