Harbeth 40.3's. Should I buy them?

Agree you don’t want speakers that are too big for the room. If so it means you can go with smaller Harbeths and maybe save some $$$s. Right size it as needed!

I auditioned 40.2’s at Deja Vu audio in Northern Virginia a few years back.  Top notch sound BUT it was in a sizeable room with speakers about 1/3 length of room out from front wall and well away from side walls as well.  Not something just any room might accommodate.  It was also with some very large and very expensive CJ tube amps.  So it better have sounded top notch and in fact it did. Bravo!

What I meant by writing "size does not matter" is that I'm not concerned with how big a speaker is in my room, only that it plays well.

And the consensus is that the 40.3 is simply too big for my room.

I'm thinking of the Devore Fidelity Silverbacks as a speaker that might work well. Or Legacy Audio Focus SE.

From what I've heard from otherwise nice Harbeth speakers, if you want to rock out, these are not the best choice in any reasonably sized room regardless of the amp.

Bigger Proacs & ATC's that I've heard are much more capable kicking some butt when desired. 

For myself, who also enjoys true dynamics & good quality loud rock music at times as well as rich, accurate sound, I have & really enjoy my highly sensitive Volti Audio Rivals! W/ good tube amplification. They are not hard or bright but big & full bodied, super dynamic,   image very well & sound like live music. They will handily out rock just about any speaker you can think of that sounds anywhere near pleasing & non fatiguing.  

They are pricey, about $15 - $18K built very well & imo, worth it. They're younger sibling, the Razz (Stereophile class B if that matters to you) is less than half the price & really nice too & will also rock out when desired.  I doubt Greg Roberts will do a home audition period but you may be able to see & listen to both of them in an upcoming show. You might really enjoy them. 

Consider looking at the NSMT Model 100.  Getting very positive reviews and are about the same price as the used 40.3's.

A bit of a different speaker, as it as an active sub in them - but could be an advantage in your room as you can then adjust the base as needed.

One reviewer called them "40.2's with balls", if that helps.

Call Ty Lashbrook at Tyler Acoustics Phone: 270-691-9500. He will gladly help you .