I have no idea what you're talking about when you mention "I know it's high-contrast vs low-contrast, Made in Germany vs Made in Japan, flare-free vs flarey, etc.".
All I can tell you is that the ZM will eventually wobble. And that's the worst thing that can happen in a lens. When a lens of mine develops a wobble I wanna smash it on the concrete instantly, without thinking. I just hate it.
I have no ZM lenses anymore. All Leica.