On the subject of the 200-600G, if you guys knew how many times I've had that thing in my basket over the last 12m
When I got my Sigma 150-600c I wasn't as into bird photography as I am now and of course back then there was no Sony 200-600. So it's become pretty much my favourite genre of photography since and I use my Sigma 150-600 all the time, it's proved the best value lens I have bought for the amount of use it gets. So, what puts me off the 200-600 you might ask? Well the price is kind of a turn off being more than double what my Sigma cost, size annoys me a little, I know most people love having internal zoom for sealing benefits but I can chuck my Sigma in and A7iii in a small backpack when I head out to walk the dog and the Sony lens would require more planning/bigger backpack etc. On the positive side, the autofocus for moving animals/birds including in flight would definitely have a higher hit rate with the Sony lens. I don't see much difference in sharpness or image quality in general but that's subjective and can depend so much on so many variables. The sample variation really worries me too.
I guess I would like to see Sigma and Tamron release something native that went to 600mm, but looking at how Tamron have massively overpriced their new 150-500mm lens I am holding out less and less hope in that area. I think for now I will carry on with my Sigma and MC-11....
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Anthony Andrades, on Flickr