Remmber that overclocking and underclocking isnt a warranty. But given that we know who the chips regulary perform we can make accurate predictions.
In both of the two situations youve stated they modules would be using Micron D9GMH chips. Such chips can do 667 CL3, 800 CL4 and 1000 CL5 at 2.2+v
Remember to always research on the specific modules youll be buying to have a more accurate parameter about their potential.