I run the C7s and I personally love all of the Harbeth speakers. You cannot go wrong with any of them. The M30 however is a reference quality monitor closely linked back to the BBC LS5/9a. I was also a huge fan of Rogers so quite familiar with that spec. I personally prefer the M30 as it is more appropriate for a home setting. The M30 is quite revealing and the bass is lacking at low listening volumes. Resolution is very good - much higher than P3 or C7 but I liked the added warmth of the C7. Now one way to fix the slight mudiness of the C7 is through cabling - I use a full loom of Nordost Blue Heaven and Purple Flare.
So for the OP, if you are using high powered/high end amp and like the resolution ,get the M30 (and the custom stands). Otherwise the P3 is a superb mini for listening a reasonable levels (they don't play loud).
So for the OP, if you are using high powered/high end amp and like the resolution ,get the M30 (and the custom stands). Otherwise the P3 is a superb mini for listening a reasonable levels (they don't play loud).