I think a larger speaker in that size room would be overwhelming. I have owned the Harbeth C7 and the M30.1 and I preferred the P3 in my 20x15 room sitting 8 feet away. About 3 weeks ago I pulled the trigger on a used pair of the HL5 with TonTrager stands figuring if they didn’t work out I could resell them without a loss.
To my surprise these are the best sounding Harbeths that I’ve owned. The seller found them bright but I sure don’t. You never know until you try a speaker in your room and gear how it will sound!
BTW, have you ever listened to the P3ESR?