How to Fix Trackpad or Touchpad speed in Linux Mint (Specifically for ThinkPad xx40+ models)
You might have noticed your trackpad or touchpad was too sensitive or fast in Linux Mint, especially on your newer ThinkPad - but not on other distros like KDE Neon or Ubuntu 18.10.
Turns out - those other distros are simply running a newer version of libinput or the kernel.
To fix it:
On a clean install of Mint: Run System Update, and do NOT attempt to change any mouse speed settings before doing this - I suspect that those changed values will be respected rather than the new ones. Install all updates and reboot.
On an existing install, I can only hope that setting your mouse/trackpad settings to default and THEN updating everything will work.