Help with high end bookshelf speakers

@OP - Do you need to put the speakers on an actual bookshelf? The room isn't that small so unless there is no floorspace, you could look at floorstanders too.

@renosteve I think @macg19 makes a good point, not only about Harbeth, but other bass-capable stand-mount, or bookshelf speakers, their in-room response betters their specs, and the Harbeths are easy to drive— a desirable quality. 
​​​​​​@yoyoyaya Mentions floor-standers, which I favor, and which also don’t take up any more floor space than stand-mounts, and supposedly deliver better bass response than stand-mounts; the argument for stand-mounts is that they offer greater flexibility in managing room modes generated by the long standing waves of bass notes. With stand-mounts and a sub or two, you are much better able to tune the room. You have something in the toolbox the floorstander can’t duplicate. 
Another argument for stand-mounts is that they are reported to image well. 
 

Were I given the opportunity to start over in a room you describe, which closely resembles the temporary home of my system, I would go with stand-mounts and a relatively high-end sub (or two) that allowed for infinite phase adjustment. 
 

Final Note: In support of the stand-mount for the space, in my nearly square, five-doored, room with a large beam / ductwork splitting the ceiling reflections up, I find that a capable full-range floor-stander (B&W 801M Series 2; front-ported, 12” woofer, separate mid/tweeter enclosure) is a little ‘big’ for the space; compared to a vintage full-range ‘bookshelf’ (Warfedale W70E; 15” woofer, 5” mid, Mylar tweeter) in the same space. The B&W has a fuller, meatier tone (or timbre), but feels a bit constrained and not ‘good.’ I think more space would allow them to open up. The Warfedales image wonderfully, and the 15” woofer digs just a bit deeper than the B&W but lacks the B&W’s ‘slam.’

Motion Audio 100 bookshelfs have a wide frequency and can go deep without the need of a sub.

If you are looking at true high end, look no further than the Sonus Faber Guarneri. They are the best sounding bookshelves I've ever heard. I shopped extensively when I bought my end game speakers. Sonus Faber should be at the top of everyone's list. I ended up with a pair of Serafinos. Outstanding engineering and the most beautiful speakers available at any price point.

Borresen M1 should do nicely