i'd choose the 96db 6 ohm Evolution Acoustics MM7's. not only are they ultra efficient, they also go down to 6 hz (-3db) and 3 hz (-6db). they combine ultra efficiency, top to bottom coherence, room adjustability and stupendous bass performance like no other speaker.
i'd add that they are superb sounding with darTZeel electronics, i use the dart pre NHB-18NS and the NHB-458 monoblocks but they also are wonderful with the modestly powered but very refined stereo NHB-108.
and i can tell you from the output readout on the 458's that most music i play does not need more than a few watts. under 10 watts does get the job done.
i'd choose the 96db 6 ohm Evolution Acoustics MM7's.
not only are they ultra efficient, they also go down to 6 hz (-3db) and 3 hz (-6db). they combine ultra efficiency, top to bottom coherence, room adjustability and stupendous bass performance like no other speaker.
I have little experience with this type of speakers, but the best I have listened to are the Avantgarde Trio horns - as far as I remember they have an amazing 109 dB/W efficiency.
If some day I would want to make a trip in the very high-efficiency land they should be my obvious choice!
the MM7's would not likely be considered affordable.....their price is 200 'large'. OTOH they do allow a system to be flexible in amplifier choices and eliminates any need to worry about adding subwoofers. they are also very room adjustable. so there is an efficiency in workability that does make them easier and cheaper to integrate into many situations. there has been lots of talk on WBF about adding subwoofers and finding capable amplifiers for over $150k speakers.....no issues on those counts with the MM7's.
AudioExplorations asked for the 'cream of the crop' of highly sensitive/efficient speaker world.