Interesting discussions on efficient speakers... I have run through the gambit of lower efficiency 87db-89db speakers and efficient 94db and very efficient 103db - 106db. And I've also gone through the same regarding the amps I believed needed to drive them. After my experiences over the past 20+ years, I moved toward the higher efficiency types (94db - 106db) with low-wattage (flea-watt) class-A single-ended both tube and solid-state amplifiers. As I moved from lower efficient to higher efficient speakers keeping my higher-powered amps in play, I could tell the difference in micro-detail. Going then from the higher-powered amps to the flea-watt amps, there was a slight but noticeable improvement in micro-detail, with no loss of dynamics or bass response at my normal listening levels. Those speakers by the way had impedances between 6-ohms and 8-ohms nominal and all had multiple drives/crossovers. Presently, I'm using a single-driver speaker with of course no crossover, that is 106db efficient with a 12.9-ohm (resistive) impedance. Every one of my flea-watt amplifiers can drive these speakers to uncomfortable listening levels with absolutely no loss of any dynamics. However, I would expect that at a 106-db efficiency, and at the rather high 12.9-ohm resistance. Even my 94-db speakers were driven with the same flea-watt amps with no dynamic compression at comfortable listening levels. I have not heard a variety of lower efficiency/impedance speakers, however in every case with the speakers I've had, the more efficient the speaker, the greater micro-detail I've heard. The only other lower efficiency speakers I've heard equivalent or better micro-dynamics, especially in the upper mid/tweeter frequencies are planar speakers. Perhaps that has more to do with the lower moving-mass of the planar electrostatics than the efficiency. Finally, one of the tests for me was the low, no-signal noise from the electronics through the speakers. If you can hear that slight noise with very efficient speakers versus lower efficient speakers, what micro-detail would you then be missing in the music with those lower-efficient speakers ? Your individual experiences may vary. This is just what I've seen/heard over the years...