People That Have Upgraded From Harbeth 30.1s....

I owned the M30.1's for 6 years and sold them after comparing to the similar sized ATC SCM19 mk2.

The ATC has a more neutral and dynamic type of sound, while still having wonderfully natural mids and highs. The SCM19's bass range is significantly more taut and punchy and - while the specs don't indicate it - reached lower in my room. Sounds more tuneful in the lows too, probably due to the sealed loading vs the ported cabinet of the 30.1's. The ATC sounds much more comfortable with bass driven music and at high SPL's too if that is your thing. They don't give up anything with vocals or acoustic music, though a less plush sound than the Harbeths. 
Both very nice speakers, but I prefer the SCM19 by a significant margin.

Worth noting that while the SCM19 has similar sensitivity specs to the 30.1 it sounds (to me) about 3dB less sensitive. Where a 50W amp might be fine with m30.1, 100W plus would be preferable with the 19's. 

@cd318 I can’t help but think you’re being a bit condescending when you infer that it might only be ’Punk or Metal etc.’ listeners who prefer say ATC to Harbeth. These are hardly genres known for their dynamics either.
For the record, a very large proportion of my listening is to acoustic/vocal dominated music - genres that the ATC Scm19’s excel at.
To me they are simply a more neutral, evenhanded speaker than the Harbeth m30.1 - which was a speaker I enjoyed for many years (in fact I’ve owned 3 different Harbeth models over a 12 year period).

If you listen at low levels and to classical/early music then I would recommend Harbeth as highly suitable.
The Harbeths are also relatively easy to drive - even a good 25W amp can sound excellent, but more watts would be better with dynamic classical progam.

@dhcod I'll be interested to read your thoughts on the comparison.
The dealer where I bought my ATC's also sells Harbeth, perhaps that's evidence that different types of listeners gravitate to one or the other, though as indicated I like both.

I do wish I'd listened to the ATC's sooner as their strengths do align better with my wide ranging taste in music. While auditioning the 19's I also briefly heard the m40.2's set up in the same room, that just convinced me the ATC's were the right move.

Great post @prof and I recognise many similarities with my Harbeth vs ATC comparison.

You're lucky you don't  live in Australia, the 40.2 currently lists for over $23K and $2.5K extra for the anniversary model.
A bit of sticker shock when I payed less than $4K for my 30.1's 6yrs ago.
The big ATC's are even more expensive, so I'll probably be sticking with my smaller monitors + sub arrangement.

The sound of 30.1 is just more refined. It handles delicate things better. Bass is less but it is punchy. The 30.1 tweeter is a tough to beat. I'm considering trying at home a set of Raidho C1.1s that my dealer has.

This was my experience too. The m30.1 tweeter endows it with a more sophisticated and complex sound than the C7ES3. In my 20x14' room I found the presentations similar, but the m30.1 was more lucid and less warm. I much preferred the later.
Some of the differences between these two may also be down to cabinet construction - the m30.1's thicker, braced, cabinet was obviously a bit different to the C7. A simple rap test showed this.