Thanks for your advice about which case to get, really appreciated. :-)
Fractal Design clearly know what they're doing.
A couple of minor niggles during the transition, but nothing to complain about.
Totally unconnected, but there just happened to be a BIOS update from which I was able to eek slightly faster RAM clock speeds (CAS16 from 18) and another 250MHz in the OC (3.925GHz from 3.9) - all stable under stressing.
There's still a few things to do (like, where can you actually put an RGB strip in a Mini C without it looking garish?), but for now, here it is - the freshly migrated
Q-bit; now Q-bit II-bit.