I’ve owned both and set them up side by side. I did not find much difference in efficiency in either one. BTW, I preferred the 3's in my 20x15 size room so I kept them!
Harbeth P3's or CS7 easier drive
I'm driving the P3's with a Croft phono Integrated. It's a very nice combo, and I would think very hard to beat for the money. Opinions may vary of course. I can't help but wonder if the C7's would unleash the Croft a bit. I remember the dealer playing the SHL5's for me after the P3's, and they easily sounded more efficient...Played louder with same amp and VC set the same. That was what I had heard about the 5's, so no surprise there. The C7's are spec'd at 86db, while the P3's I believe are 83.5db. However, the Harbeth site suggests an amp with higher wattage (than P3) for the C7's. Cheers -Don