Hi,
new here but I'll post my humble opinion.
I seem to remember that Mr Shaw, on the HUG forum, once posted that the so-called special version of his speakers - read: 30th anniversary, 40th anniversary and so forth - where special binding posts or internal cabling were used, were just answers to distributors' and retailers' requests. He made it clear that he did not care much for it personally.
I have heard the SHL5, the SHL5+ and the SHL5 40th a number of times. The XD series is less clear to me. In my opinion, all the series after the first are sort of afterthoughts. They sound slightly different from each other - the XD series especially. It seems to me that Mr Shaw worked to give his speakers a more 'modern' voice while retaining the classic thin-wall design and the basic sound. I do not like the XD series and in general think that the 'classic' SHL5s, if driven with a powerful and clear-sounding amp, are the best of the bunch, and preferable to the subsequent versions. I mean, if you want the Harbeth sound why go for some re-thinking?
That said, I don't think that a really good loudspeaker - one that sounds good with any recording, any source, any amp - really exists. Loudspeakers are the most difficult choice and the most severe compromise we do when assembling a system. Harbeth can be a good domestic companion, provided one loves the austere voice and the non-hifi presentation. Mr Shaw also posted, on many occasions, that more watts are always desirable and that 'only a fool wouldn't want more watts'.
Best,
H.