You asked
Olympus m zuiko 75 300mm f 4 8 6 7 ii vs panasonic 100 300mm f 4 5 6?
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 Wildlife and sport: Reach: Focal length is the first thing to sort out. - Sport from the sideline and larger animals: 70-200mm to 100-400mm on full frame. - Birds: 600mm full-frame equivalent and beyond. Birds are small and far away; a common saying is that you never have enough reach for them. Smaller sensors help here. A 100-400mm lens on APS-C gives the view of about 150-600mm on full frame, and on Micro Four ...
Quoted from this site's pages.