Nothing on the market beats the Sony sensors, except MF Sony sensors
But the 5D4 is a big improvement. I find noise wise it is far superior to the 5D3 and due to all the pixels I can also keep the 1Dx in the bag when shooting at ISO6400 (down sample to similar res and the noised is very similar). When shooting up to ISO1600 I just love the files.
Despite the AF being fast and perfectly usable at f8 (100-400 II and TC) and with a full spread of points, there are situations that just confuse it, such as back lighting and dull days with less contrast (which is odd as in low light it beats my 1Dx) even on my 200-400 f4. I had this confirmed by a few people too.
I went into the 5D4 knowing that it had some big limitations. The buffer is one. OK until you are in a situation when it is not
Only allowing UHS-I cards did not help. Fast CF cards are OK but I do find 4K video will stop whereas on a half decent SD card it is way more stable. Would rather be investing in CFast cards at this point than old tech. Not that I do much video, this camera is not really made for it, or is crippled not to do it
I mean seriously, wanted to do some 4K of a goshawk eating on Sunday and I was too close
A couple more FPS would have been sweet too, and yes it is possible... see A99II for reference
That said one reason I bought it was noise, the 1Dx is like a train when shooting, the 5D4 gives me a little stealth which I needed more than I expected this winter when goshawks turned up to feed and still are.
But as we already know it is a "do it all" body. If I did more landscapes I would be using the A7rII already but 30MP is plenty for what I do, having no AA filter may have been nice though.