Canon 50 1.0 on Canon 5D2
Leica 50 1.0 on Leica M7
I used to own the Canon 5D2 when the only AF lens I had was the Canon 50 1.0 AF. It was a great lens and a very nice camera. I did have a couple of converters so that I could use my Nikkor AIS glass on it. While the AF on the 50 1.0 wasn't blazing fast, it was deadly accurate -- at least, my version of the camera/lens. Manual focusing the Nikkor AIS glass was possible but could have been better with a different screen with some contrast. I got the camera to get my feet wet with HD video. And since you have to focus using the chimp screen, the viewfinder is irrelevant. Being able to zoom in on the big, bright and beautiful screen is a big plus on static subjects but isn't any help for moving subjects. In that case, your skill with MF is all you've got. Use the back screen in bright light and you've got your work cut out for you.
While I don't own an M9 yet
😉, I have used one and I'm familar with the focusing patch. In my experience, it's very accurate and the only trouble I've ever had is with shots like the one with the shoe. The busy foreground/background made it tricky.
I agree about contrast being the ticket for ease of focusing with the rangefinder system. In low light like the shot I posted of the wall, which was a 30-second exposure, the difference between the shadow and the wall was all I needed to nail the focus. The same with the big machine behind the gas station.
As far as IQ between the Canon 5D2 and the M9, you have to consider all the links in the image chain (lens, focus, camera shake, processing ...OO) and that includes the photographer.
I think what it comes down to is you have to figure out which camera is the right one for you.
50 1.0 Noctilux on Leica M9