Most coherent low volume speaker with very fast bass under 10k used?

For 70db & medium sized room
+ matching amp recommendation please
"The amp used to drive the speakers is more important to how fast/well controlled the woofers etc.. "

Couldn’t agree more amplification and cables determined the quality of the drivers control ,it’s better to invest your fonds on good amplification and cables with decent speakers than buying suppirier speakers that you can’t afford the proper amplification to drive and control them.
I have the Rockport Aviors and I find them very coherent. They play particularly well at low SPLs. However, I my view, they need good quality, high current amplification to bring out the best in them, especially at low volumes. As such, I second the view that you should focus as much on amplification proposed to be used as much as the speakers - the two are not mutually my view
I've had great pleasure from my Monitor Audio PL100 II. Those are 6k new. If you go up the list to the slender floor standers you'll find speakers you could get well under 10k used.  I find the Monitor remarkable, and much better -FOR MY TASTE-- than Totem, Kef, Focal, etc.
You also might look for Aerial 7k. I listened to the smaller ones and found them quite good. 
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I didn't see in your posts what type of music you listen to.

I listen to mostly classical and jazz at relatively low levels, even at night while I'm sleeping.

Some time ago I discovered Meadowlark speakers which are sadly no longer being made, but for me provide exactly what you're looking for.

I bought (used) five different pairs: Swifts, Kestrels, Ospreys, Swallows, and Kestrel 2s.  I find them all to be wonderful, and you can usually find them pretty cheap.  I got the Ospreys shipped from Texas to New England for $1500.  They're gorgeous and I wouldn't trade them for many of the new speakers being made today.

 Good luck in your quest.