No CPU or motherboard supports 2133MHz RAM if not overclocked, So, if you don't plan to overclock... you will only pay more for 2133Mhz RAM.
If you do buy 2133MHz RAM, and don't overclock it, it will slow down to the CPU and mobo supported speed of 1600MHz for Intel Core i3, i5, i7 CPUs... 1866Mhz for higher priced Core i's,.. and 1866MHz for AMD CPUs.