I'm considering getting a Metabones T-Smart adapter to mount a Canon EF 200 f2.8 L II to my GX8 as a compact wildlife package. I have been using my 100-300 for wildlife. It's great lens. With the 200 f2.8 I would have the field of view of a 400mm on my GX8 and a stop and a half more light gathering. I always shoot wildlife off a tripod so my primary concern stopping movement of feeding animals in low light conditions. I'd be interested others experiences with the metabones t smart adapter..... Www.timothyharrisphoto.com
As barry said with the 100-300 you have a field of view maxing at 600mm with the 200mm it will be 400mm,now better IQ possibly from the 200mm would alow a image crop but i doubt it will bring you up to the 300mm level.
Comparing the 2 lenses at 200mm, the Canon is f2.8 and the Panasonic is at f4.9 which is 1.5 stops. That was my thought process....
