Hopefully in the future I will be able to post more in this thread. So far the one and only shot with GFX as I had to send it for repair, turns out I had an unfortunate lens communication error on my body.
Here are a few birds shot with 645Z and the lovely, cheap FA 200/4. These are not the best bird pictures you have seen, I'm guessing - but I merely wanted to demonstrate the capability of that $300 lens. I think I'm getting more pixels per duck than I did with my old Canon 1DX + 400/2.8L IS, with the 51megapixel 645Z + 200mm lens.
Below each picture I'll post a link to a higher resolution photo, 50% smaller than original, and uncropped.