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

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!

I had SHL5s some years ago and didn't really like them - I found them rather soft and woolly sounding, particularly in the bass. I sold them and moved on to something else for a few years.

More recently I came to hear the M30.1s and ended up buying a pair. I love them. They are far more neutral and natural sounding than the SHL5s in my 4 x 5m room. Bass is not all that deep, but it is tight and rhythmic. The M30.1s are also more extended and cleaner in the treble, and the midrange is more refined and more transparent.

So, personally, I would consider the SHL5 a downgrade from the M30.1s. But I wouldn't discourage you from hearing them - they may just be what you are looking for. But I agree with others that an amplifier or source upgrade may be a better option.

The M30.1s are truly amazing speakers and I would be interested to know why you are feeling the urge to upgrade them.