Question: can ddr4 2400 run at 2133?
Answer: Yes it can be done, but you need to keep in mind that you will work on 2133MHz also, you should be having same type of DDR i.e.3 or 4 or 5 etc. Also, if you managed to overclocked the 2133 to 2400 then both will run on dual channel with 2400MHz & in this case it will be some what better then 8 GB @ 2133.