A few random notes for you. I've never had C7ES3's but did own some P3ESR's while I owned my Omegas. As you surmised, the Harbeth sound is very different than that of Omega. Harbeth's are warm and smooth speakers and can even have a tendency to make everything sound better than it is. I found that over time, this grated on me because they sort of had a homogenizing effect. Everything sounded very good, nothing sounded bad, but nothing sounded as spectacular as I thought it could either.
Omegas can be at the opposite end of the spectrum and be ruthlessly revealing. All of the sudden, a recording you may have enjoyed with the Harbeths, you won't with the Omegas. The Omegas however will really reward you when you play a good recording with fast transients, great microdynamics and a cohesiveness that can be unsettling at times.
Most speakers today have a bass hump around the 60 to as high as 200 hz range. We've all become accustomed to it and truthfully, many people like it. The Omegas don't and how you react to this will really ultimately determine if you like them or not. What many people think they are hearing as low bass really isn't, it's part of that hump. With Omegas, there is no added fullness or bass and at first things may sound "light" to you. You either will get used to it or not. When I had my Harbeths, I always found it difficult to go back to them after listening to the Omegas. It took a few listening sessions to get re-accustomed to their sound. Switching back to the Omegas was like going back to an old comfortable friend and I'd adjust very quickly.
As far as ultimate low bass, my guess is that the Harbeths will certainly sound and go lower than the CAM's/SAM's.
I do have a pair of the Zu DW's and I would say that they hit somewhere in between the sound of the Harbeths and the Omegas.
Good luck with your journey.