Current or Previous Harbeth Owners…

NOPE!
 Only the Sonus Faber Toy Towers I had even come close to the performance of my current M30.2Xd's & even those were not quite as transparent through the midrange...

I previously owned 40.1's and 40.2 Anniversaries.. preferred 40.1's fwiw.

I found YG Carmels were more enjoyable/musical than M30.2s in a medium sized room powered by Luxman L-590 AXii. Not by much though, and they’re 3 x more expensive. Harbeths are hard to beat, depending on what you listen to. In the same room I preferred M40.2 to Magico A3 with Luxman separates. In my current room I prefer Focal Kantas. Not as natural on voices but all around better soundstaging, bass and highs; more linear. Musical enough, and easier to pair with amplification. I haven’t had the M40s though in my current room, only the M30s. I’m sure if I had the right amplification and set up there’s a good chance I might prefer the M40s to the Kantas.

If you’re thinking about M40s, just make sure your room is big enough.  My original room was 14 x 21 feet, and while the 40s sounded great in there, ultimately they were just too big, too much bass.  I went from the 40s to the 30s in that room.  

Have I heard speakers that impressed me enough to consider a possible replacement for  my M30.2 XD’s?

Yes and No …. Let me explain …

NO: Nada at its speaker current pricepoint nor even if you double it and a bit more,…..

YES ….. but only at significant multiples in speaker price-point step-up AND (a fine and important distinction …) a stablemate many multiples price step-up for the rest of the upstream audio system electronics . (My system is in the $40k - $50K range ) 

I do not know your Harbeths, but become increasingly convinced there is so much to improve upon in front of any transducer in the way of not only equipment, but power conditioning and cabling.  My transducers (3 years now) continue to improve markedly as power cables and interconnects break in.

I've invested considerably in equipment stand, floor stander platforms, wall outlet and of course room treatment.  I believe many of us go down the rabbit hole chasing ghosts.  Those Harbeths being quite good may well have not reached full potential with what's in front of them.  Or, I could be wrong.  Cheers