I used MSI Afterburner (windows)
If you haven't tried it, don't forget to change/add to your afterburner.cfg:
UnofficialOverclockingEULA = I confirm that I am aware of unofficial overclocking limitations and fully understand that MSI will not provide me any support on it
UnofficialOverclockingMode = 2
EnableUnofficialOverClocking = 1
Everyone seems to mention it's as easy as adding the eula portion and setting unofficialoverclocking mode = 1, but that never works for me.
After you add these lines, you can lower clock, close msi afterburner and reopen, lower it again, close reopen and keep doing this. MSI Afterburner doesn't allow you to lower the clocks too far without having to close the program first.