Best $4000-$5000 loudspeaker

- Price range from $4000 to $5000, new or used.
- Room average size.
- Average efficiency (or good, of course).
- -3dB at 40Hz or better bass extension.
- Capable to be enjoyable at low listening levels.

Opinions are welcome. I have not introduced higher constraints, so that opinions suit other enthusiasts.
Regards and thanks.