@prof and @arthur1260 -- thank you for taking the time to provide such detailed and helpful replies. I truly appreciate it. The truth is that I'm quite happy with my SHL5+ and have come to appreciate the qualities that Harbeth brings to the table -- and I say this after owning and auditioning several speakers. That's why it has been such a difficult decision. But like @prof said, there are always tradeoffs. And sometimes the only way to find out is to try something in your own house. I will try to listen to the speakers in the seller's house as best as I can, but I understand that it's not quite the same as experiencing in your own setup. Unfortunately, buying from a private party means I can't just return the speakers if I don't like the sound. It's unfair to the seller.
I also want to address the concern regarding which wall (short or long) is going to be more suitable. Keep in mind that even the short wall is 15 feet wide, and I can easily place them about 2.5 feet from the side walls and 4 feet from the front wall. Given the layout of the room, and the fact that it doubles as a media room as well, I don't really have a choice but to utilize the short wall for this purpose. However, I have had other speakers in this room and I feel the short wall just works well. IMO, distance from the front wall is much more important than the side walls, especially for rear-ported speakers. Plus I've treated the first reflection points quite well. But I guess there's only one way to find out. BTW, my SHL5+ sound fantastic in the same position.
Reading the responses above, my fear is that I might lose the amazing vocal reproduction and that special texture that made me fall in love with Harbeth in the first place. I just hope I don't end up regretting my decision. But it's encouraging to read all the other qualities that JA Perspectives bring to the table. I also don't like thin sounding (especially in the midrange region). That's the reason I never liked Focal or B&W type of speakers. Not saying that they are thin sounding but they do sound that way when compared to Harbeth or other BBC-inspired speakers. If that turns out to be the case, then I definitely know I wouldn't be able to live with them long term.
I'm going to go listen to them on Friday. I'll keep you guys posted. Again, thank you for your very helpful feedback.

