If you want efficiency, then Klipsch is at the top of the list. You can't go wrong with around 100db Cornwall's with a tube amp. They play low volume full bodied music or blow your roof off rock & roll with ease. Forte's and Heresy are basically mini-me Cornwall's and do the job just as well.
BUT
Spatial Audio Sapphire M3 open baffle is the reason you buy a two channel Macintosh integrated amp at 100wpc (AKA MA5200/MA5300) or the top contender according to you, hook up the speakers, and end your quest for the holy grail of audio sound so you can finally think about other things you want to do in life!.