I've ran 85 db efficient speakers with my Torii with great success.

My every day speakers are 89-90 db efficient and they can make your ears bleed in my room.

There are so many factors. I protect my ears from really really loud sound so I never push my system into really "LOUD" playback. Yet with my 92.5 db HR-1 loudspeakers when I have the system to the very top end of what is loud for me I still have headroom. Crossover, room size and listening position, personal top loudness level, hearing--all play a part, and more.

The sad limiting factor is that if you don't find an amp works for you and need to return it, you could face a looooooonnnnnng wait for another Decware amp to replace it. That's the current Decware reality we face with brave resolve. Perhaps the situation will improve, I do harbor hope along those lines.

I'm very happy with the levels of playback I have in my systems and that the single-ended components produce them.

I honestly don't think "db" efficiency is an earmark or factor of "quality" in playback. Different designs yield both different "character" and efficiency, and though one could perhaps say that there's a general nature to a high efficiency speaker's sound and a low efficiency speaker sound, I am certain that "quality" exists in both extremes and in between.

Compatibility and synergy between amp and speaker is really important, and yet even that is not a certainty that can be prescribed with authority as two persons with the same amp and speaker combo could have differing opinions on the playback due to so many other factors such as power, isolation, speaker positioning, listener positioning, hearing, and the type of playback a person prefers.

There's certainly an element of "taking a leap of faith" in audio selection. Even going to Decfest and hearing something, that "something" may be significantly different in one's own room. I've made a lot of leaps, and learned from them, so that there is less "guesswork" for my own rooms and wants and likes.

2.83v is 1 watt into 8 ohms and I’d bet the 86dB was measured at one meter, on axis.

I had tried out a set of B&W towers in my old home for a couple of weeks.
Published at 84dB efficiency. With mono'ed Zens, they sounded pretty good.
They were loud enough and had good mids and crisp highs. Just not really my cup o' tea. They sounded compressed, bridled, hindered, hobbled. Super flat, though, if you have to have that.

I've been listening to open back speakers since before the turn of the century and I have become a bit spoiled to the "no box" sound.

I still keep some powerful boxes around, but I generally only pull them out for others these days.

I did not buy the B&Ws.