The speed of the ram does not matter , you can put 32gb in there if you want to. The question is why would you , do you have some applications that use a tremendous amount of ram? You will not even use half of it for gaming , any game. If you want to get the best use of that speed and all you use the Pc for is gaming then get 8gb of the 2133mhz ram , if you want to go higher then get 16gb. I have heard that the computer uses the ram more efficiently if all the slots are not populated and the max amount is not installed.