The title should be self explicative. I'm gonna pair the Ryzen 9 5900x with 128gb of DDR4 (4x32). I have found two options, both compatible with either of the two possible mobos I am going to get (CH VIII Dark Hero, or Aorus Master, x570 of course), according to their respective QQL lists:
My rig will be used for both video editing and gaming, with the occasional streaming and certainly lots of multi tasking.
Shall I go for higher frequency or lower latency? And would it be possible for you to explain why?
You can calculate the actual latency to compare.
Using the examples you provided to compare the CAS latency 16@3200 vs 18@3600, actual latency is 10ns for both.
Calculate by multiplying the CAS value with the clock cycle time. E.g for the 3200MHz kit, the clock rate is actually 1600MHz because it's DDR RAM. So you would calculate with 16 * (1 / 1600000000) or simply 16 / 1600000000 to give you 0.00000001 (10ns).
Likewise for the 3600MHz kit, 18 / 1800000000 = 0.00000001 (10ns).
This means both kits will have the same actual CAS latency (for delay sensitive workloads they will be the same, but the 3600MHz kit will have higher bandwidth (for throughput sensitive workloads, the 3600MHz kit will provide more GB/s)
Deleted my answer after checking the QVL list for both Motherboards. I answered before on my Cellphone and was unable to check the QVL lists.
The Asus Motherboard both the 3200 & 3600 Mhz RAM is listed for 4 slots while the Gigabyte Aorus Master version 1.2 it only shows the 3600 Mhz as being compatible in 4 slots but not the 3200 Mhz.
I do know for best performance that the sweet spot for the Ryzen 3xxx processor is 3600 Mhz for RAM Speed while the sweet spot for Ryzen 2xxx Processors is 3200 Mhz.
But I don't know the sweet spot for the new 5xxx Processors.