Speakers with the most detailed midrange? (non-ESL/planar)

Look for speakers that use drivers that are actually pistonic throughout the midrange (and treble, too).  Price no object, Vandy 5 and 7mkii, as well as most of the Vivid Audio stuff.  

It is likely that the new Paradigms with the beryllium midrange are pistonic, but I'm not sure (and haven't heard them...they seem to bit a bit divisive based on comments I've seen here).

It’s probably going to be a three way speaker, as the given two way speaker will have some minimal issues of some sort in the frequency range you specify.

That the frequency range you specify is almost the exact full covered range of a given average three way’s midrange driver.

It is also, for some basic acoustic and technical reasons.... the hardest part to get right.

This is the big money range, where the mid driver, if done as best as possible.... might start to touch $1k or more in costs.

It’s just plainly, a brutal set of incongruent requirements, a set of mechanical, magnetic, and electrical complexities where the pairing of that with acoustic issues, all fight against one another and individually within themselves.

That’s a midrange driver.

It makes tweeters and woofers look easy. And they’re not.

How far did they have to go to get close?

It’s a standard high end loudspeaker designer’s dilemma: Walking through the endless desert, begging, crying, looking for ---a perfect midrange driver.

+ 1 ATC. Their 3 inch super mid range dome practically owns the mid range and has done so for 30 years. Many have tried to better ATC but all I have been weighed, measured and found wanting. Still being installed by professionals in million $ facilities to this day.

I have heard good things about the Gallo Acoustics Ref 3's and the Strada. Very electrostatic midrange.

“It is also, for some basic acoustic and technical reasons.... the hardest part to get right...”

My experience as a listener is very different. I find even very moderately priced 2-way speakers have little trouble reproducing the so-called midrange sound. Of course without specifics, e.g., frequency range, etc., “midrange” means different thing to different people but sounds like human voice reading a book or even middle octaves of an instrument can be reproduced quite well by just using a decent single driver full range speaker system. I think it’s the transients in music like going from low to high and visa verse that will require multi-way speakers.