yep you can.why run it on low if you have 2133 mhz freqency ram with you as most likely system will set it to 1333mhz.Ram frequencies dont matter much in gaming or practically anything unless you are rendering something in photoshop or during video editing process.Things will get faster a bit though just a bit.Check if the 2133 is overclocked frequency or your ram's default one.If its overclocked one set in on 1866mhz.