And on emacs. I have "turn on/off syntax highlighting" as a shortcut. Specially useful for largish JSON files, for some reason emacs chokes easily on them

I like how you say "on emacs". Makes it sound like "on Windows", i.e. Emacs the OS... ;)

Well, I'm not native so on and in are somehow hard to pinpoint. Quite likely I'd have said also on vim :) (I use emacs+evil by the way)

Emacs has (or maybe had, I didn't check for a few year) a hard limit which is 512 MiB on 32 bit platforms.

Here's my list of commands for large files in Vim, but I'm no Vim guru:

    set nobackup
    set nowritebackup
    set noswapfile

Also, from the Vim Tips wiki: "Faster loading of large files" http://vim.wikia.com/wiki/VimTip611

One can turn off syntax highlighting only for long lines in vim.

    set synmaxcol=N_characters