High vs. Low Efficiency Speakers

I do not think it is possible to generalize. I have heard a few high efficiency speakers: Lowther, Tannoy, Avantgarde, and Zu. And I have heard a few low efficiency speakers as well.

In general, low efficiency speakers have a brutal kind of sound. These are typically very linear sounding, with ample bass. The sound from these speakers are typically very impressive. But as we all know, impressive does not necessarily mean they are musical.

The high efficiency speakers I have heard, without exception, suffered from problems. The Tannoys have a lazy coloration that kills the rhythm of music. The Zu's sound distant and uninvolving. The Avantgardes have horn coloration. The Lowthers are beautiful, but lack treble and bass extension. (Yes, I know this is a gross generalization but it is based on the systems I have heard).

Of all the high efficiency speakers I have heard, the Lowthers impressed me the most. But that is my particular musical taste (classical). YMMV.

To echo Duke's take on dynamic contrast. I used to own lower efficiency speakers (Sonus Faber Extrema, Dynaudio Confidence 5), despite their fine sound quality, it takes mega watts to create the jump factor that mimics live music. I later moved to higher efficiency speakers, not 95db but something real world in the 90+ range. Now I can run tube amps which sounds better to my ears, more lively, more micro dynamic, more enjoyable.

I was seriously considering MBL speakers for some times, but despite the huge soundstage it creates and superb imaging, it lacks the high efficiency speaker jump factor and I will never be able to run them with tube amps. you know the rest of the story.

for classical music at low volume, I highly recommend high efficiency (95+ db) and SET amp. I can see myself listening to big Tannoy with SET glowing in the background and my face grin from ear to ear.

i own a pair of montana xp speakers they are rated at 92. i think that is pretty efficent and the sound very musical with any kind of music you want to play. they have awsome slamming bass. awsome midrange and treble

Are there benefits / disadvantages to either?))
Typically ext ream High efficient speakers with multiple drivers in the same pass band tend to achieve their
amplitude or efficiency at the expense of clarity by smearing which in my opinion sounds worse at low volume.
A well designed point source speaker with an easier load for tubes would be what I think you are looking for.
((I listen primarily to classical and prefer tube amps, does this lead me toward one speaker over another?))
I would take a look at the more well known mainstream successful high end designs that match your preferences.
((Lastly, I try to keep the music at a fairly low volume -- need to protect the hearing!))
Just remember a coherent speaker wont need the treble jacked up to balance fix the bump in the bass

If you like tube amps, a high efficiency speaker with a benign impedance curve is a no-brainer.

Regards
Paul