I keep thinking to myself I've got way to many guitars and not enough 300mm 2.8's. Time to raise some $$$$
Been wanting the Sony 300mm real bad for a long time. I have a love hate relationship with the the 200-600......love it for video on my FX3, not so much love in terms of photography on my A7R5's. I've had a couple copies of the 200-600, both excellent.....really really good with ample light but most of my wildlife action happens at or near the dark and F6.3 in low light with the shutter speeds you need just doesn't cut it for photography.
However and where the 200-600 really shines is in terms of low light video on a body like the FX3 where you can just about shoot video in the dark at ISO 12800 which cleans up very good in post. I think I'd actually prefer the 200-600 for video over even a 300mm 2.8 or big 600mm f4. When you have deer at 20 to 100+ yards and everywhere in between at the same time just before dark the zoom (even though slow) covers you bases like a champ on the FX3. FX3 is simply a low light beast for video. Just need a better low light photography solution and pretty sure its going to be 300mm 2.8. Have to sell to many guitars to get the big 600mm f4