Murphycat, guess what. I switched from Harbeth SHL5+ to Graham LS5/9. Both good and rather close in sound signature with BBC heritage, but they sound different.
I listened to both M30.1 and LS5/9 separately in different systems, and I now own the latter. I felt the M30.1 is a warmer sounding speaker with a fuller and thicker midrange. Generally the sound with the Harbeth is warmer and less airier with a in-the-room feel. Dynamics leap out from a blacker background with the Harbeth. The treble with the 30.1 is slightly rolled off. The Graham LS5/9 sounds less restrained, airier and more open. To me, the Graham is less colored than the Harbeth.
In my experience, the Harbeth pre-XD models have a warm sound signature. I was told that the XD series although a bit brighter still have the warm "Harbeth sound".