I follow that completely.

MBPs use 1066MHz RAMs for older models, 1333 for those around 2011-ish, 1600 for 2012 upwards, etc. Hence, my question.

EDIT: AFAIK, MBPs can use lower speed RAMs – upgraded my mate’s 2012 to 8GB 1066MHz. Slight performance hit but lower heat/power observations.