I'd argue that 64GB is not enough. I was surprised to see that level of memory.
I imagine 4K video at 60fps would eat up a lot of that 64GB.
4k video using hevc actually helps cut size down a lot. 64 is still not very much but should be good enough for most people, especially if they rely on icloud.
Solid upgrade. I'll hang onto my 6s and my wired headphone ways a bit longer though.