Large Room which speakers?

How far you sit from the speakers is as important as room size. Also depends on what your idea of "fill the room" is. I would suppose the Hornings do have enough gas in the tank to satisfy most in a room that size, but still would have their limits.

I don't have a room that large, but if I did ...

I would go big on the speakers, based on the information you provided:

Big Duntechs, Magneplanar 1-D, Sound Labs, Genesis, Quintessence, Wilson, Pipedreams, etc.

A lot will depend on your listening position. If you sit reasonably close to the speakers, your choices are plentiful. If you're twenty feet back, that's a different kettle of fish and you'll probably want something a little bottom heavy. If you're moving around and the listening position is unpredictable, then wide dispersion might be beneficial. Therefore, you might want to think twice about narrow dispersion, horn loaded designs like (I believe) the Hornings. Further, if you really want to energize that entire space, you'll need to consider the speaker's max SPL capability.

In your shoes, I might think hard about the big MBLs, if you can swing a pair and the required amplification.

Please do yourself a favor and ask ONE person.....at an audio store near you. Try and find someone you like and trust who may even go to your house and see your room. Everything from cables, to room conditioning is in play here. Every room is different. The one nice thing about speakers like Vandys with the built in subs, is that they allow you to set it up easier in regards to best placement for the mids on up and then you can just dial in the bass and you still don't lose the coherency like you will using subs. I'm sure there will be five or more on this thread alone who will disagree with me and that just shows you that you need to find someone you trust and listen to them. Most on here have been around audio for some years and we all have our own likes and prejudices. The one thing that most will agree on is that you can't just say, what are the best speakers.....Synergy is what makes audio magic. The amps, pre amp, sources, electricity, room, cables.....did I miss anything? I'm sure I did. These are all different when they are set up with different components. Often times you can tune a room with a well placed rug and or large plant in the corner. What state are you in? If you share that, you will get many of us who probably know someone good to refer you to and you can go from there to see who you like and trust.