I put this in my ~/.xsession

    # keyboard autorepeat delay / rate
    xset r rate 170 30

It's tuned to my personal typing to be just slow enough that I never have accidental ddoublette kkeypresses, but fast enough that I can just hold down 'j' or 'k' in vim to move 10 or 15 lines (and easily hit the target). Using the mouse cannot even come close here (assuming you don't have your hand on it already). 15 lines would be 620ms here technically, so including the human factors it's still comfortably below a second. Really it makes a huge difference. (I saw this first in a talk by Edward Kmett).