speaker endgame upgrade recommendations coming from Harbeth C7ES-3 XD2?

Not sure about “end game” and I have never heard the 40’s, but IMO, the SHL5s were a significant upgrade from the 7s and I did do a direct A/B at the dealer. Bigger, fuller sound with more satisfying bass, but with the Harbeth vocal accuracy you appear to value. I have also owned the P3s and M30s and I personally preferred the SHL5s to either by far. I. have also owned several fine speakers, including the Totem Forest, Hawks, Chartwell L6s, Trenner & Friedel Pharoahs and Audio Note Ks.  I liked all of them, but the SHL5s had the most realistic vocals, IMO.  But I also felt that they were extremely sensitive to stands. I found that open- frame metal stands worked best, but I never heard the Tontrager wood stands that people seem to rave about. I would try to audition the 40s if your really looking for “end game,” but I think you would appreciate the SHL5s, at least as an interim upgrade. 

   Among conventional box speakers, you have two basic camps—modern “high-tech” speakers using technology and modern materials to kill resonance from drivers and cabinets and those who employ resonance even if this is “messy” and does not measure well.  Many British Isle manufacturers are in the “messy” camp, like Harbeth, ProAc, Graham, Tannoy, and Audio Note.  In the USA, companies like Devore and klipsch have models in both camps.  
   I tend to like “messy” speakers more because they sound lively and musically natural.  I don’t care that much that bass tends to be not as tight or extend as deep.  A lot of modern speakers in the other camp sound dead and need to be played at higher volume levels to have some life; “constipated” is another term used for that sound. 
   My other preference related to lively sound is higher efficiency.  Many of the fery best amps are low-powered and high efficiency helps with finding a good match. 
   For specific recommendations, it is hard to say without more details on budget, room size, speaker location limitations, etc.  But for a rough guess, I would suggest Volti Audio (quite good horn-based systems), Devore, Audio Note, Graham, Fyne, Charney Audio, and Songer Audio.  
   A dealer in my area used to carry both Harbeth and Audio Note speakers.  I found it interesting that most of his new, walk-in customers came to hear Harbeth, not Audi Note and many did buy Harbeth, but of those customers who listened to both brands, many switched to Audio Note; there were not many coming in for Audio Note that went the other way.

The drivers on this cone-based speaker are unique and, in my opinion, better than Beryllium based drivers. Same detail but no harshness. It is my end game speaker so much so that I tossed the shipping boxes a few years ago. 

Yamaha NS-5000PNST 3-Way Bookshelf Speakers with Stands | Hi-Fi Heaven

Yamaha NS-5000PNST 3-Way Bookshelf Speakers with Stands | Hi-Fi Heaven

Spend the saved money on a top-class powerful amp for these speakers. 

Ive owned too many box speakers and several OBs. I much prefer OBs whose money goes into part not coffins

I had a pair of Harbeth 30.2 XDs for a number of years, but ultimately upgraded to Joseph Audio Perspective Graphens. I am fairly sure the Joseph's are in your price range.

While the Harberths produced the kind of accuracy and transparency I value, the Perspectives take both of those to the next level. They are considerably larger than the Harberths and the resulting bass performance is notable. But for me, it is the fluidity and detail that have made the difference. 

The good news is that in the $20k price range, you have an enormous range of options, probably too many if I am being honest. Hearing more about what you listen to and source would be helpful, but in the end you will want to spend some time listening in person. 

Good luck with your search!