I have unlimited data also but have a 128gb iphone.
Undecided on the X but whether to go for the 64 or 256 if I did, still yet to use even half of my 64GB storage, roughly 25gb until that point .
So 64GB might be fine but it might be better to go overkill and get 256 just incase.
Pricey either way but obviously 256 is more
If you can afford it, go for the 256GB.
It’s always nice not having to worry about storage space.
I’ll be replacing my iPhone 7 Plus. Hopefully this will take place in 2017.