What about installing 2 Memory module pairs of same size but different clock-speed?

Question

I know there are questions about installing RAM memory modules of different sizes, but I have now a different situation I didn't have before, and I can't find any information about it.

My motherboard (Asus M5A99X Evo R2.0) supports DDR3 RAM-memory modules at 2133(O.C.)/1866/1600/1333/1066MHz.

At this moment I have two 1866MHz RAM-memory modules (2x4GB), installed on A1+B1, but due to CPU specifications, they work at maximum supported rate of 1333MHz, and I would like to add 2 new RAM-memory modules of 4GB each (to be installed on A2+B2), but I cannot find the ones I'm looking for (actually they are just too expensive), I find only DDR3 1600MHz. (All of them are Non-ECC/unbuffered, and are supported for my motherboard: [QVL], but there's no word about installing RAM-pairs of different clock-speed per pair-channel).

Are they gonna work at 1333MHz all together without any problem or is it a trouble-situation?

Answer 1

As the CPU does not support OC RAM, according to you, they will all just run at 1333MHz. More important are latencies like RAS-Latency, CAS-Latency, RAS-to-CAS etc, specified in numbers like e.g. 9-9-9-27. It is better if they are the same.