For the lenses you use, the M3 can be the answer to your prayers. See how to lay your hands on one and be amazed at how it looks with a 50mm lens attached; it's like the whole viewfinder is your field of view. It's also nicer to use with long glass (I have an Elmar collapsible to use with my M3 body), but things change if you want to use anything wider than 50. I think there is only one wide-angle for the M3: the Summaron 35mm (can be f2.8 or 3.5) and has goggles (and needs to be used with them always). I recall there being a 'cron 35 too (with goggles).
Otherwise, if your 35mm lens doens't have goggles you'll need a separate VF to figure out the field of view.
So, keep that in mind... and silently lean towards the ZI. It's beautiful, BTW, and feels nice in the hand. 🙂