I currently use a Leica M10-R and have used each one of the predecessor Leica M cameras before the M10-R was released. I also have other digital DSLRs, including a Nikon D850. It's difficult to compare a digital rangefinder Leica M to a DSLR -- they are simply different tools. I personally like the simplicity and deliberateness of a manual focus rangefinder, but for me one of the best reasons to shoot a Leica M is to be able to use one of Leica's world class lenses. The dynamic range of the M10-R is superb, and the image quality of the 41 MP M10-R is at least equal to, if not better than, the 47 MP Nikon D850. For sports or other fast-paced activity, or scenarios where I need a longer telephoto lens and/or autofocus, I'll grab the D850. Everything else, I prefer the Leica M10-R.

A Leica M rangefinder is not well suited to every task, and to be sure, a manual focus rangefinder is not necessarily for everyone -- especially someone who has known only DSLRs. A Leica M subtly forces you to slow down and think about the basics -- composition, all of the exposure variables, etc. And that slower, more deliberate process sometimes leads to a better result. Can you achieve the same result with other camera? Yes, of course, you can, but there is something "special" about shooting a Leica M.

I started with Leica M film cameras and still shoot my Leica M6TTL (as recently as yesterday . . .). If you like your M6, I can pretty confidently assure you that you'll like -- no, love -- the Leica M10-R. I think it's the best digital camera Leica has ever made, and I personally can't see how they can improve on the M10-R. Obviously, whatever glass you current have for your M6 will work just fine on the M10-R.