The hummingbird garden has been really busy. The hummingbirds are storing up energy for their flight across the Gulf of Mexico. I bought the Fuji 100-400 for situations like this so I could get closer to the action. My technique is to focus on the flowers, not the birds. What I need from a lens is to be able to have pinpoint accuracy. I have the smallest focus point selected so I can get focused on particular points of interest. Because the flowers are staggered at different depths, I need the lens and camera to be able to focus at various points depending on where the bird goes.
I have pretty much given up on trying to follow the birds in action. I couldn't even do that with a Nikon D3s. My technique of focusing on the flower where the bird has resulted in higher keeper rates. The 100-400 paired with a fuji x-t1 does a pretty good job of this. It isn't in the class of a sports camera, but it is close. I am more than satisfied with the IQ wide open and even with the 1.4 TC.