Executing vim commands without interactive mode

I would do:

find .... -print0 | xargs -0 vim -c 'argdo set fenc=utf8' -c 'wqa'

linux unix vim encoding

Filetype, syntax and indent plugins are probably what's slowing you down.These are specified in your ~/.vimrc with a line that looks typically like:

filetype plugin indent on

You could try commenting that out, or
You can start Vim without your plugins and ~/.vimrc but staying in nocompatible mode by doing:
vim -Nu NONE

CodeHunter