avanti,
From my auditioning the 30.1s are more even and controlled through their frequency range.
When I auditioned the 30s I really liked their sound, but wished for some deeper bass. The C7es3 did that and I liked it for the bigger sound, but found the bass to be a bit overwarm and less tight than I'd like.
That's why I ended up owning (for a while) the Super HL5Plus which were for me the perfect version - bigger and more full than the 30s, but also the best controlled and most balanced bass of the line (not to mention, more realistically open and extended on the top end, without losing the Harbeth midrange magic).