from Harbeth 30.1 to SHL5+, an upgrade or lateral move?

To me, the SHL5+ is somewhat of an outlier in the Harbeth line.  It sounds quite different from their other speakers--it has a more modern, conventional sound (not as warm, tighter sounding and punchy bass).  I like the SHL5+, even though I don't like most modern speakers, but, the only Harbeth I really LOVE is the 40.2 (very much NOT a modern sounding speaker). 

I've owned the Monitor 30s and the SHL5s and I really think it's a matter of taste.  The 5's have a bigger, fuller sound that some might describe as less "accurate" than the M30s.  The 5's are also more forgiving of lesser electronics, IMO.  Depending on your setup and room, the differences could be minimal.  Frankly, I would want a home audition before dropping the kind of money they're getting now for the 5s.  When I bought mine they were 4k.  

Unless you are ready to step up to 40.1's, I'd keep the 30.1's and get a decent subwoofer, as that will get you closer to the 40.1 sound than buying SHL5+.  I've owned the SHL5's (non + version), and am now on my second pair of 40.1's, which I love and have no intentions of selling.  The SHL5's were nice, but not in the same league as the 40.1's IME.

I moved from the C7ES3 to the SHL5+ and it was certainly an upgrade. I will never buy a pair of 40/1 as long as I live because they're too large for my room. I'm also running a REL B3 and a class A Accuphase so things aren't too shabby around here. If you have plans of some day purchasing a pair of 40.1's, I'd keep what you have an get a sub like pdreger suggested. Ultimately an in home demo would be your best bet but we know how hard that is.

Thank you for your valuable advice. I dont have chance to audition, all I can is read comments, reviews and order from audiogon, ebay... that's why all your answers are of great help to me. So for now,I guess I will buy a sub or upgrade amp, source for 30.1s. I the future when my budget for audio is bigger I will think about 40.1s :). 
Thank you again!