Andrey, before leaping for an M-Series, for your purposes a screwmount (or "Barnack") Leica might be a better choice. They are considerably smaller, and if you are using a wide lens with an auxiliary finder, the M-series' advantages diminish. And the lenses you are considering can be mounted on either body. If you can get to a store that has both in stock, you should handle both before settling on the M-series. You might find that a Leica IIIa or one of its cousins feels better in your hands, and will save you several hundred dollars as well.