Vandersteen 3a signature vs Harbeth 30.2 anniversary

@OP,
If you are working with Johnny, then you are in good hands already.
I didn't know he carried Harbeth. I'll go for a demo next time.

And, if you are open to adding a sub, then as @joey54 said, the Quatro's are probably the 'sweet spot'. I wonder if Johnny can add subs to the Treo's in the demo room? Those little VLR's with a Sub 3 really kick a** with the Belles Aria integrated and the William Tell cables. 
Bob

If you can find a used pair of 40.1 or 40.2 you should be all set.  The 40.1's wouldn't be all that expensive.  Don't forget either about the Spendor SP100 series--like the Harbeth 40's, there are differences between the different iterations.

John has a Sub3 hooked up to the Treo's now.

You may be better off with the M30.1, versus later models, should you remain interested in the smaller Harbeth monitors but seek the classic British midrange magic.  Spendor 2/3 or larger, along with corresponding Graham monitors and floor standers also might suit your interests.  Good luck and happy listening. 

All, responses have been great and helpful. Nice to have the information.Definitely have some listening to do based on suggestions.
The Harbeth importer is is southern NH so I can see some time there having a listen and will try to get back to JohnnyR to revisit the Treo’s and subbed 3’s.
The used Quatro was previously on my radar after last years Treo listen based on some of the same logic I’m sliding into with the Harbeths that a bigger step up will be more of a definite than something that is a bit lateral or logically the next step. I did lurk a bit looking for used Quatros last year but they seemed pretty scarce versus me being a bit surprised at looking for used Harbeths yesterday and finding several that seemed to be solid.
Work, the good kind, to do here. Should be a fun and interesting journey.