I realize this is an old post, but I noticed some odd behavior on Kubuntu 19.04 that might be of interest to anyone thinking of switching from the Green Team to the Red Team:
If you've been using the NVIDIA proprietary driver, hell if you had even installed it but didn't use it even, completely uninstall it! Like full-on Purge that *****!
Whatever the Linux Mint equivalent to these commands are:
sudo apt-get purge pkg && sudo apt-get autoremove
Do that. Either together as typed above so the second command runs if the first is succeeds or you can run each command individually. Whatever you choose, I'd say it's best to remove all NVIDIA drivers before switching cards, so you will be on the native display driver; otherwise, your CPU usage will have at least one of the cores locked at 100% ALL THE TIME because Linux can't reconcile the fact that you are using a different vendor's GPU & no amount of Killing or Terminating the NVIDIA **** will help, cause within 2 minutes of doing so then BAM, just like that your CPU usage is back to running flat-out & your CPU cooling fans are screaming along at full tilt trying to keep things cool.
This would seem like common sense, right? While, I did remove the NVIDIA driver (using the Package Manager, though) before swapping cards, I jumped the gun a little & installed the AMD Radeon driver & software (again through the Package Manager) before going Red Team. Don't ask me why, probably got a little excited thinking I'd be able to actually play some games seeing that I haven't been able to since making the switch to Linux. Long story short, I'm back on Team Green since I still wasn't able to play any games & my NVIDIA card is FAR less power hungry, runs at the very most a mere 5 degrees C warmer than the Radeon card without having the fans run at 15% to keep things from warming up the case needlessly & the CPU utilization is back to more sane levels & will actually drop down to idle levels or with a low load & temperatures will be comfortably below 36 degrees C while merely surfing the Interwebs & jamming tunes.