I echo much of your experience. After much experimentation I've found the second monitor very helpful in a broad range of tasks. But I've ended up with an asymmetrical setup, whereby my main monitor is a full HD one (an AOC 21") and my secondary one my laptop's native 1366x768.

This allows me to focus on what I am doing (in the main monitor), while the secondary one holds any reference material, related emails etc. If nothing else, I will keep there TheBrain open, to remind me of what I am working on if I digress...

Ken wrote:

My preference for two monitors is
that it offers some flexibility, especially if you need one or both in
vertical orientation (something that I personally do not use). I can
understand the appeal of a single monitor if you are doing heavy reading
as part of your work, although I am not sure how much more head turning
there is between a large curved monitor and two smaller ones next to
each other (similar to what you have shown in your photo of multiple
monitors). I do read while I write, but mostly in short bursts. And, I
have not tried Moom as I am on a PC, but I find drag and drop really
quick and easy as I can leave windows open and just click and drop as
they are needed. I was never a fan of windows that partially occupy a
monitor, but I know that is a common set-up for many. Also, regarding
head turning, I set in a chair that swivels, so I guess that I am not
turning my head as much as my whole body. I am not sure if this
information is helpful as you move forward in your decision process, but
I hope it is of some value.