Capslock is an Escape key for me because I use Vim a lot. I've heard lots of tmux users map it to Control and then configure tmux to use Ctrl+a as the activation mapping, which sounds very useful too.
A default vim mapping is CTRL+[ I use that a lot as it requires the smallest motion of my hands. The fd seems pretty cool as that's even a smaller change. How do you set that in your .vimrc?