The limiter is actually how well the RAM is binned...sort of like CPUs, the memory chips on the stick can be of better or worse manufacturing. This depends entirely on the "silicon lottery", so some RAM may OC from 1333 MHz to 2400 MHz, while other RAM may go from 1600 MHz to 1866 MHz. It's all dependent on what the RAM is capable of...it's kind of a crap shoot in that regard. Though, if you start with higher Bandwidth memory, you'll likely have better results than starting with lower bandwidth memory.