Harbeth 30.1 or 40.1

Thanks for all the reply.  I believe the only way to find out if I will the Harbeth is to buy one and use it at home.  Although not yet audition the Harbeth, based on my past experience, it is not that useful; because the room is different, the amp, the source ... everything are different.  So, my approach is buy used, bring it home, and if it doesn’t work out, I will sell it out hopefully won’t lose too much.  
It seems now the determining factor is the price.  Not only the 40.1 is more expensive, I believe it needs a more powerful amp as well which is also more expensive.  

@mapman can you please elaborate on your experience between the Spatial and 40.2?  Which model of Spatial you hear?  Are they in different settings, different room and different equipment?  
Since the Spatial is open baffle, I hope or expect it gives a bigger sound stage and more life-like.  This is one of the reason I buy it, and it is true compared to my Zu Omen Def MK I.  The X5 has a big Air Motion Transformer for high frequency of 1k and up.  It provides more detail and sound more transparent than the Zu, but at the same time, I need to be careful about pairing equipments.  For instance, I bought a Toppings DX7 pro which also offers all the details, and I feel fatigued after an hour of listening and need to turn down the volume.  
By comparing YouTube videos and my X5, I believe the Harbeth gives warmer sound.  But I hope it also gives the same level, or a bit less, of detail and clarity.  I expect the soundstage May get smaller.  I hope the instrument separation is still good.  

@gte357s

Yes, totally different setups in all regards. Very hard to compare concisely other than both were top notch in their own way in my opinion, though much different.

Harbeth 40.2 was at Deja Vu Audio in Northern VIrginia in their large showroom off their top of the line Conrad Johnson amps. Spatial (not sure of model) was at Capital Audiofest 2018 in an average size hotel room. Do not recall amp used but was more modest as I recall. The designer/owner was seated right next to me and we chatted as I listened.

The biggest difference was in the overall presentation and soundstage as one might imagine with two such different designs with different dispersion characteristics.

The Harbeth presentation was unique in that the speakers were set up a good 1/3 of the way into the room, and there was good soundstage detachment and some depth but not all the way back towards the rear wall as is often the case with many less boxy modern speaker designs. Donna Godchaux’s vocal on Sunrise from Terrapin Station album struck me as particularly spectacular with the Harbeth streamed from my home library via Plex on my Smartphone using whatever high end DAC it was they used. Maybe Audio Note?

I think " warmth" will vary with gear used. The demo I heard surprisingly did not strike me as warm sounding, more neutral with very good detail and no fatigue.

I suspect both sound their best with room to breath but should work fine as well in tighter quarters. In tighter quarters, I suspect the largest Harbeths might be a bit of overkill. They are very good sounding large box speakers, but I have to wonder how some other similar larger size box designs I have heard over the years for way less cost would fare against them. Overall they remind me of old Ohm model C2 speakers, which I also used to like very much, but listed for $700 or so a pair back in the 1970s. Of course I never heard those running off large high end tube amps like the CJs at Deja Vu Audio back then so again apples/oranges. I wonder.....

I’ve heard Zu many times at CAF and they have yet to grab me.

The 40.2's at Deja Vu were, for me, the best audition--the best-sounding speakers--I've ever had in an audio store.  After just a few seconds of a Beethoven piano concerto I let out a "wow".  If I could have 75% of that at home I'd be a happy camper.

I'm less sure about the 40.1 but there isn't an absolute need to drive the 40.2 with more than 60 or 70 quality watts.  Yes, perhaps more is better, but quality is also better or quantity.

You'll need to add sub(s) to the 30.1 to get the bass quality of the 40's, so something to consider when considering financial outlay.  I agree, though, that you can only ultimately tell at home with an audition there.