it says 2000(oc) since that is the highest officially supported by your motherboard.
dont worry about "official", its very likely your board can run higher anyways.
just get 2133 ram. if your board wont push them that fast it will just downclock them.... at which point you can just tighen up the timings... basically you can downclock the 2133 sticks to run at whatever you want, 2000@cas9.... 1866@cas8 maybe.