You asked
Olympus m zuiko 75 300mm f 4 8 6 7 ii vs panasonic 100 400mm f 4 6 3?
Here is what the site says about that.
From Olympus M.Zuiko 75-300mm f/4.8-6.7 II: Olympus M.Zuiko 75-300mm f/4.8-6.7 II: A zoom lens by Olympus for Micro Four Thirds cameras, 75-300mm f/4.8-6.7. A small, light 150-600mm-equivalent telephoto zoom. Specs - Maker: Olympus - Focal length: 75-300mm (zoom) - Maximum aperture: f/4.8-6.7 (it gets darker as you zoom in) - Made for: Micro Four Thirds sensors - Mounts: Micro Four Thirds - Stabilised: no - Autofocus: yes What it frames like - On Micro Four Thirds (Micro Four Thirds): like 150-600mm ...
From OM System M.Zuiko 100-400mm f/5-6.3 IS II: OM System M.Zuiko 100-400mm f/5-6.3 IS II: A zoom lens by OM System for Micro Four Thirds cameras, 100-400mm f/5-6.3.
Quoted from this site's pages.