Best 40 to 50k used speakers

Wow, what a nice budget, especially, for a used pair of speakers!
You should end up with something extraordinary~

I spent a few minutes with the responses; no surprises there.
All wonderful recommendations...everyone has an opinion.

I wonder where you could go to audition more than one example of something in this caliber?
Traveling can be tricky these days, but I would hope you would want to listen to as many possibilities as you could find? "The journey's the thing"

I didn't see any mention of Gayle Sanders finest effort with his Martin-Logan Statement e2
What a spectacular system! The design, the presence and the sound quality always blew me away!

Arnie Nudell's Infinity IRS-V is another remarkable speaker (once the woofers have been replaced) Paul McGowan at PSAudio can attest to that...

I 'second the motion' regarding the original Nautilus' (I owned the 8th pair made for over 15 years) what a wonderful experience!
However, they require 8-channels of amplification for the pair, so you really will need another large budget for power...

I wonder if 50k would buy a nice pair of Wilson Audio Alexandria's?
That another pretty great speaker~

Remember, regardless what speaker you decide on, you will want multiple subs to go along with it~ regardless. 

Have a great time with this...
Stay well and safe; best regards,
Jim Gray
Jim Gray Designs
jimgraydesigns.com

I'd buy the best used Estelon speaker I could afford, even if I had to wait for newer models to becomes available used.  There's something deeply satisfying in their presentation of music.

I can 2nd the recommendation for PMC MB2 SE if you have the room - they play everything wonderfully at all volume levels in my room - but if I was going to buy these again - I would go with active instead of passive - even though I’m extremely happy with my preamp / dac and amps - 

My two cents, I have a pair of Alexia (1), Borresen O-5 and am not far from France ;-)

Assuming the $40K - $50K is your assumed new speaker price, I went through a similar exercise a year or so back. Also, we have about the same size rooms. My top contenders in no particular order were:
- Vandersteen 7 Mk II
- Vivid Audio Giya G2 S2
- Evolution Acoustics MM3
- Wilson Audio Alexia Mk II
- Magico S3 Mk II

After hearing all above I purchased the Giyas which, to my ears were the most cohesive (blending of drivers), effortless at any level, accurate (not warm or sterile) of the bunch. I may have bought the Vandys if I could have found a pair used. I think I liked the Vandys highs better than the Vivids but the Vivids play louder more effortlessly and cleaner than the Vandys. YMMV