GH3 with 100-300mm
Have you tried ETC mode with this lens?
When I get a new camera, especially one as capable as this one, I start with the basic settings and only move into more advanced user features as I get better with the basics. So far I have concentrated on focus box settings, AFS/AFF and MF, and drive modes. But I will give ETC a try because that certainly would "reach" out a lot further.
And, for some reason unknown except maybe masochism, I've decided to master the GH3 WiFi. That works but requires a LOT of experimenting and failed efforts.