Horn Speaker Recommendations

@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?

I have not heard the speakers by Volti Audio, but they would be on my list of speakers to audition should I ever have that kind of money.
https://www.youtube.com/watch?v=Q8hU4tDnZ7I&feature=share

OP should realize that he is definitely going to have to settle for a hybrid horn speaker in his price range. A full range horn by the very nature of its size and price is not likely doable for him. Also, some of the brands thrown around in this thread like Cessaro are going to be non starters as well due to price.

My advice would be that if you're going the horn/hybrid route, get as much of the sound as you can get out of the horn part of the speaker. In other words, look for something with a low xover point where the "hybrid" turns over to the horn. Many of the models recommended in this thread and virtually all of the two ways will have xover points so high that most if not all of the bass and midrange delivery will be coming from the "hybrid" box part. My two way JBL 200s of yore were that way. The 15" driver didn't hand over to the horn loaded tweeter til right at 1000 hz. The 15 incher was handling all of the bass and midrange duties.

Enter the Avantgarde Duo. As a three way with active bass and a default setting of 160 hz (user adjustable) from subs to midrange I now have over two more octaves of horn delivered output as compared to the JBLs and many of the other models suggested in this thread. The difference in the unfettered expansiveness and palpability of sound as produced from the bells of horns rather than the typical box is immediately obvious to anyone, So, to sum it up, horns, yes, by ALL means but preferably speakers where the horn(s) is playing the lead and not second fiddle to "the box".

@acresverde --

OP should realize that he is definitely going to have to settle for a hybrid horn speaker in his price range. A full range horn by the very nature of its size and price is not likely doable for him. Also, some of the brands thrown around in this thread like Cessaro are going to be non starters as well due to price.

Size may be a problem, but with a price range up to $40,000 a truly capable all-horn setup is absolutely within reach. Remember, all-horn items from Cessaro and the likes are steeply priced, and oftentimes all-horn speakers represent a manufacturer’s statement products, for no other reason really than keeping them out of hand from any but the most well-paid. There are all-horn main speakers like Volti Audio’s Vittora’s (around ~$20k sans Gregs DR subs) or Simon Mears Audio Uccello’s (£10,500 direct sale from Simon, but being a busy man at present sadly doesn’t take orders), and couple either of those with the likes of a pair of Danley Sound Labs tapped horn TH-50 (unaware of their price, but with named main speakers would come in under $40k), or the front loaded horns like JTR Orbit Shifter LFU (independently tested here: https://www.data-bass.com/data?page=system&id=123):

https://www.danleysoundlabs.com/products/subwoofers/tapped-horns/th50/

http://www.jtrspeakers.com/orbit-shifter-lfu.html

These are all pre-build solutions (though you would need amp + digital XO for the TH-50, but they would still fall within the price ceiling), but don’t mistake the horn subs mentioned for being blow-your-roof-off capable only; they offer excellent bass quality all around, and will provide effortless performance for any purpose and at SPL's few would be able to endure (not meant as a quality in itself, but that it grants you effortless presentation at any SPL). In combination with all-horn speakers like the ones mentioned you’d be in for something sonically quite special.

Then there’re DIY horn sub solutions that I mentioned earlier in this thread, and couple those with DIY all-horn main speakers from John Inlow and you’d come in under $10k for the whole shebang.