As if a D500 / D850 would give you 7 or 10 frames per second in perfect focus 
. Sorry Dave, but that's definitely not happening in my experience, and that goes for the Tamron, the Sigma and for the Nikkor 300/4 (with active VR) as well. Especially the engaged VR will throw your focus point often off target.
The Z 6 should be a bit faster in aquiring focus, but the Z 7 is nothing to write home about in terms of speed - and it is not meant to be a speed-giant anyway. But if I manage to engage tracking (in my eyes far too complicated compared to the simple 3D-tracking), this tracking will cover the whole frame - of a full frame, not your tiny D500
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And then, α9 and X-T3 are at least 3rd generation bodies. I can't speak about X-T1 or X-T3, but X-T2 needed 4 major firmware upgrades during 2 years to get to a usable AF-C - which still lacks a feature I often need: Manual override, when the bird sits behind twigs or hidden behind reeds is impossible with an X-T2, and the reach of the 100-400 sucks as much as the focus limiter or the misplaced manual focus ring.
So, in ML land the α9 rules. For now... But both Chris and Barney had a hard time in a low lit soccer arena. The fact the 200-600 doesn't extend is something very welcome.
Btw. the 60-600 is better than the 150-600 sports at the long end, and less poorly balanced, too, as the extension tube is made of plastic and the hood as well, so much lighter than it's heavy metal brother.
. Sorry Dave, but that's definitely not happening in my experience, and that goes for the Tamron, the Sigma and for the Nikkor 300/4 (with active VR) as well. Especially the engaged VR will throw your focus point often off target.The Z 6 should be a bit faster in aquiring focus, but the Z 7 is nothing to write home about in terms of speed - and it is not meant to be a speed-giant anyway. But if I manage to engage tracking (in my eyes far too complicated compared to the simple 3D-tracking), this tracking will cover the whole frame - of a full frame, not your tiny D500
.And then, α9 and X-T3 are at least 3rd generation bodies. I can't speak about X-T1 or X-T3, but X-T2 needed 4 major firmware upgrades during 2 years to get to a usable AF-C - which still lacks a feature I often need: Manual override, when the bird sits behind twigs or hidden behind reeds is impossible with an X-T2, and the reach of the 100-400 sucks as much as the focus limiter or the misplaced manual focus ring.
So, in ML land the α9 rules. For now... But both Chris and Barney had a hard time in a low lit soccer arena. The fact the 200-600 doesn't extend is something very welcome.
Btw. the 60-600 is better than the 150-600 sports at the long end, and less poorly balanced, too, as the extension tube is made of plastic and the hood as well, so much lighter than it's heavy metal brother.