I bought the wife an M5, it is extremly light and takes great pics. I have been interested in trying the adapter and macro, just haven't messed with it yet. The downside is really bad battery life. The AF is great but not fast at all. Because it has the main screen on the back and you are viewing through the view finder it eats the battery fast. I wonder if the M6 is better on the batteries. Maybe someone that owns one would chime in.

You are not going to shed weight unless you go to a smaller system. Maybe someone knows of a different system that would be lighter and handle noise better, but I think your 6D is toward the top on that respect and anything that is better is going to be heavier.