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

The SHL5 Plus does not sound soft and woolly as the SHL5. The bass of the SHL5+ is fuller, deeper, tighter and punchier than the M30.1. The largest difference or transformation between the SHL5 and SHL5+ is in the bass department apart from better integration between the drivers which in turn produces an overall smoother and more coherent presentation.

the shl5+ extends lower and have better bass overall. id say its a upgrade to go from 30.1 to shl5+.

I agree on many above and think that the shl5+ is like a 30.1 (wonderful midrange) but with deeper bass and more 3D feeling. I would want switch some day.

I'm shopping Harbeths actually too; after auditioning the 7s, 30.1, 40s, and SHL5+; I found much of the feedback in this forum to be spot-on.  I'm finding that selecting the "right" Harbeth to be really music, personal taste dependent. I listen to classic rock and really like the bass extension and treble of the SHL5+ compared to the other Harbeths, very noticeable.  I second the "sub" suggestion for consideration if you're satisfied with most of your music genres and the 30.1.

To Rossb: The type of music I listen to is classical , jazz, vocal, pop. I agree with you that 30.1 has a very refined and natural  midrange. However, I feel the urge to upgrade because the soundstage of 30.1 is not wide (it could be due to my small room: 12 x 15 feet) and contrabass in jazz sounds weak and thin, which makes the song does not have the necessary bass. 

Do you experience the same on your 30.1 pair? I am using Quad 99 and 909 for it.