Please help me choose
I decided to buy 5Diii or 6D
Can I have a try giving an advice? In my opinion, the best buy is 5D3, because it is the best camera for ML and especially for shooting an uncompressed video (losslessly compressed, more like zip, rar or whatever). You can use the fastest SD and CF cards, overclock the SD controller with sd_uhs module and use the card spanning mode, when 5D3 writes on both cards simultaneously. Thus you'd be able to shoot in the highest definition possible. Non-anamorphic 1-1 mode is 3K and anamorphic full frame mode is 5.7K if I'm not mistake, all 25fps, thanks to Danne. You can also shoot in 1080p full frame binned mode. You cannot shoot 5.7K or even 3K with 6D continuously. I can do that with 5D3 with SD Sandisk Extreme Pro 64 GB 170 MB/s and CF Sandisk Extreme Pro 128 GB 160 MB/s installed.
So, I'd like to advice you to buy 5D3.
The key point is that you have to choose the 5D3 with the Canon firmware version 1.2.4 or less, to be successfully downgraded to 1.1.3 or 1.2.3. I was a lucky because I've bought the cam with 1.0.4 firmware, so I had to
upgrade it.