looking at these I dont think it matters too much which of the cameras you use that are in the 5 to 6 year old category, they all seem very capable and I find it strange that many people i know are scared to go over ISO 1600 with one of the latest cameras!!! It all comes down to ability to process and know your own camera
Agreed! I've shot at ISO 16000 on my Olympus E-M1, carefully overexposed the image just before highlight clipping, and pulled it down in post and it looked fine! I know it's all personal preference, but if it's possible to get good images out of a five year old micro four thirds camera, then shooting at ISO 12,800 on a 5D IV shouldn't be a problem at all.