depends on the motherboard chipset and the cpu you use. the newer mb will take faster ram and a lot of mb vendor goof on there product labeling. if you do have a older cpu or one with a speed limit the mb will read the ram spd info and set the ram speed to 1333 speed. (667). 1600 ram is just 800 speed ram so your not losing much in speed. (if the mb defaults to 1333 and is an intel or amd see if it run at 1600 by turning on xmp profile).