Pasting a huge amount of text into vim is slow?

This is a buffer flush-to-disk problem. Vim tries to keep your work safe and doesn't assume you can type several thousand characters per second. Read :help swap-file for some details on the buffering. The solution to your problem is this:

Turn off vim's swapfile either with:

vim -n <your file>

or from within vim before the paste:

:set noswapfile

See :help swapfile for more details.

Another option is to simply turn off the syncing to disk of the swap file with :set swapsync= but this option takes more keystrokes to undo and I'm lazy. :)

Turning off swap is not safe for normal operations! Immediately after the paste, either use :set swapfile or :set swapsync=fsync to revert back to normal behavior (though technically, normal behavior might have been sync and not fsync, check with :set swapsync? beforehand if you want to go this route).

Use "*p or "*P to paste from the system clipboard instantly.

Vim must be compiled with +clipboard for this to work.

See :help clipboard for more information.

In my experience :set syntax=off helps before pasting, see https://askubuntu.com/a/223061/240577 I've seen 'slow' behavior/high cpu usage with vim/gvim/mvim on osx, ubuntu, redhat and windows when pasting large blocks of content and syntax highlighting is on.