So, what do I think? The R5 is more convenient to use than the D850, with the C1, C2, C3 modes in particular. The AF is lightning fast and latches on to animals incredibly well, even at a distance, and focusses fine at f/11 with the Canon lens (very slow with my Sigma 150-600mm C). The IQ is comparable to the 5DSR and better than the 5DIV. It captured the flying butterflies which I couldn't do on the D850, and it did the same with a small fast bird. The D850, on the other and gives sharper and more contrasty images with the 500mm PF and also at 700mm with its TC. It does most of the birds in flight just as well so far. Both systems are absolute winners. One thing I didn't like with the EVF is that I generally underexpose, either with an offset allowing the camera to choose the iso or by a stop or two in manual for BIF and then correct in post as for these great sensors there is no noise penalty and so I never bleach highlights. With the EVF, the image was very dark for my BIF shots. I did like being able to adjust iso while shooting, on the other hand.