I spent the morning shooting with my Lumix 100-400 set to 200mm to see whether you really can do birding and wildlife with a 20mpx crop sensor.
I was working towards getting the Oly 300/4 for my GH5 but now I am thrown into confusion by the 200/2.8. My heart says Lumix and my head says Oly.
Nevertheless I did manage to pull out some good bird photos at a native 200mm. One thing which had not really penetrated my thinking is the additional stops over the 100-400 at the same zoom focal length. In winter that is an important factor, e.g. being able to keep up to 1/1000-1/2000 even on a dim day.
Anyway, just in case people are wondering if 200mm (400mm equiv) can yield good results, this is about 50% of the frame with the 100-400 set to 200mm, iso800, f5.1, 1/5000 (electronic shutter).
To afford either lens I have to sell some kit or I think my wife will serve me with divorce papers