How important is the efficiency of a speaker to you?

@phd 

At 102db efficiency may I suggest you try SETs rather than push pulls? You might be in for a big surprise. A classic 300b amp will amply drive those speakers unless they have a weird impedance pattern

antigruge2, that is very interesting recommendation about trying a set amp. This has been recommended before and I look forward into to getting one to try in the near future.

This sounds like Wilson Audio, which I have.  Do not assume everything you read.  I recently auditioned a pair of Alexia 1 that are supposed to require lots of SS power.  The sounded better and more musical at the same output with an Audio Research 75SE than they did with a McIntosh 450wpc SS amp.  

The speakers I was referring to were not Wilson's. Nonetheless, it is interesting what you posted about Alexia 1's. They are known to be extremely difficult to drive. Is it possible that the ARC Ref 75SE has a more capable transformer, and as such can drive the Alexia's? 

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...