Its commonly known that on AMD you're better with tight timing than higher frequencies. In fact, you would sometime get better performance from running at 1333 than 1600. Just check your timing. 5-5-5-15 @ 1333Mhz and 6-6-6-18 @ 1600Mhz are the sweet spots (for now) and they are pretty equivalent, depending on what bench you're looking at. Keep in mind that 1600Mhz is OC, so some memory controler prefer not to be OCed but can take tighter timing. It all depends on your CPU IMC. Just test and see. Bench every settings and get the one that fits better your need.
