I have a pair of MP-02 Plasma tweeters that I sometimes use in summer (windows open) that I believe are capable of going to 100khz
I cross these over (3rd order) to my ML Monolith III’s at 12khz, and yes you can hear the difference, if I had to explain it’s sound, it would be an extended delicacy, with more air there, you can really notice it on harpsichord it just floats in front of you, like you can reach out and touch it.
Cheers George