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

As someone already mentioned, Proac D48r

..or if you’re looking for small and cheap, not minding limited LF, i’d recommend a pair of vintage NEAR 10m’s, which are a rare little two-way with proprietary spider-less drivers. I preferred the originals (silver woofer caps and smaller tweeters). I’ve had three pairs of these at various times in my life and they are great cheap little near-field monitors and certainly decent otherwise. Very transparent, revealing. You might have to get the woofers serviced but the original designer, Lewis Athanis, might be able to offer some assistance. He’s helping me restore a pair of the larger NEAR 50’s. The suspension ferro-fluid he uses is a special sauce and he’s got quite a creative mind regarding audio if you happen to chat with him.

or these are also good if you honestly don’t mind ports...

http://greenmountainaudio.com/rio/

Under 12K, in my experience, Hands-Down the Paradigm Persona 3F at 10K per pair: 99.9% pure beryllium mid-range is extremely fast, so much so that it can do intensely detailed sounds with soft edges to them; very well balanced across the audio spectrum with its high sensitivity; extremely well-reviewed.

I second Evolution Acoustics. I own the Micro Ones and they are fantastic for midrange detail. Pair them with two subs and they become a powerhouse. The thing that make these spectacular though is what electronics you put behind them. The company only uses Dartzeel to showcase them, but I’ve heard them with various quality electronics. You can’t go wrong with these little gems.