Hey Alan,
Last weekend I spent two days in the Parc de Marquenterre nature reserve in France and was able to test the Mark2 in real life.
For me, I couldn't see a clear difference in detecting birds from the R5 to the Mark 2 version.
But what there is a clear difference for me is the tracking ability of the new focus. This means that the eye autofocus allows me to select a sitting target much more quickly and to create the composition the way I want with a quick pan of the camera.
I also find that the tracking of birds in flight is clearly better, so you get much more sharp images.
I think this can be seen most clearly in video mode. Here the focus is extremely quick and you hardly lose the bird from the plane of focus, which was often a problem with the old R5 (often a lot of focus pumping).
This was also one of the main reasons why I bought the Mark 2, as there was a significant improvement, especially in the video area.
I'm already looking forward to winter, when I'll try to catch the kingfisher diving again when the lake is almost frozen. I think the Mark 2 clearly beats its predecessor here, especially because of the precapture.
Unfortunately, there is still little denoising software that supports the Mark 2.
However, you can also work with Topaz Foto AI software using Photoshop and the results are very impressive. At high ISO I like the result better than with the R5.
I hope that the software translated it correctly into English, as unfortunately I'm not very fluent in English.