Largest Digital Camera

[KmH]

Class 10 should be sufficient for 4K video.
Nikon recommends class 6 memory cards as a minimum for video.
XQD card write speeds of 45 MB/s (300x) should suffice.

I shoot 4K video to class 10, 98 MB/s (653x), 32 GB UHS-1 micro SDHC cards.
I have 4 of the 32 GB micro cards & 2 micro to SD card adapters.