Has anyone who currently has both bodies done an AF shootout between the two bodies yet? Perhaps also against the 1Dx2, A9 and D5?
They're almost indistinguishable performance-wise and interchangeable role-wise in almost every other respect - 42MP/10fps vs 45MP/9fps, similar DR, ISO 64 for the D850 vs better high-ISO for the A7r3, pixel-shift vs focus stacking.
For shooting things that don't move much, there's not much between them.
Yet almost every review has been about image quality rather than the one feature which could really set them apart from each other - AF acquisition and tracking on difficult subjects and their performance in the action camera role.