[Keith Darby]

Not sure if you got to the bottom of your query on card speeds and why the Canon 5DIII can write video without problem to the SD card but I think the problem relates to the confusion between bits and bytes.

The 90Mbits figure that is quoted for the Canon 5DIII for ALL-I video is not the same as 90Mbytes per second – in fact 90Mbits converts to around just 11Mbytes per second which most reasonable SD cards can handle.

Check out this link for bits to bytes conversion https://www.unitconversion.org/data-storage/megabits-to-megabytes-conversion.html

And this link to the write speed comparison done by Rob Galbraith – from the RAW and JPEG write speeds to file you can see all but the lowest can handle ALL-I video – not sure if anyone has tried one of those cards from the bottom of his list and whether the camera freezes or just removes the options for higher bit rate video?