I have had the Compact 7s and now have the M30.1s. I have heard the SHL5s in my room. I have heard the P3s twice in a dealer audition. My room is a bit smaller than yours, 12x18. I highly recommend the M30.1, or M30 as stated in your original post (used, I presume). They should fill the room without overwhelming it. I have read some of the posts in response to your question on the Harbeth forum. It seems to me that the general opinion on HUG is go with the larger speaker due to its larger midbass driver. I agree.
In response to the above posts about the C7s' bass being muddier than the P3s, yes, that is true. But definitely not the case of the M30.1. You will get the "larger" sound of the C7 with the clarity of the P3.
In response to the above posts about the C7s' bass being muddier than the P3s, yes, that is true. But definitely not the case of the M30.1. You will get the "larger" sound of the C7 with the clarity of the P3.