No Keys Repeating on New MacBook Pro After Changing Key Repeat Speed
It probably wouldn't help, but you could try changing the keys directly in ~/Library/Preferences/.GlobalPreferences.plist or ~/Library/Preferences/ByHost/.GlobalPreferences.*.plist.

defaults write -g KeyRepeat -int 2
defaults write -g InitialKeyRepeat -int 15
defaults -currentHost write -g KeyRepeat -int 2
defaults -currentHost write -g InitialKeyRepeat -int 15


2 and 15 are the fastest settings shown in System Preferences. The changes aren't applied until you log out and back in.

The file in the ByHost folder doesn't normally have keys for the settings, but it has precedence over the normal .GlobalPreferences.plist.

You can remove the keys with the delete subcommand:

defaults delete -g KeyRepeat
defaults delete -g InitialKeyRepeat
defaults -currentHost delete -g KeyRepeat
defaults -currentHost delete -g InitialKeyRepeat