I have a similar question. I like the fact that the board supports up to 64Gb of RAM, an amount I may never need. But I am doing a Ryzen 7 2700X build, and from what I've researched is that the ASRock B450M Pro4's ram limit is DDR4-2666 stock, with the ability to OC to 3200. I want to take advantage of Ryzen's ability to use 3200+. Currently, I'm looking at Crucial Ballistix Sport AT 32 GB (2 x 16 GB) DDR4-2666 Memory. Having a hard time finding specific compatibility information regarding this particular DIMM and board. Also, if the board supports DDR4-3200 OC would it also mean it would support DDR4-3200 stock (I'm looking at another RAM option at DDR4-3200 with a great price). Sorry, sort of newb here, and thanks for any information. I also should note that I'm trying to take advantage of a MicroCenter CPU/board bundle.
I am not exactly sure what you are asking here, but I'll give it a shot.
Your not gonna get the Ballistix Sport 2666 to overclock to 3200mhz. There is a reason it is rated at 2666mhz, if it could run at 3200mhz, they would sell it for more.
The 2700x supports native RAM speeds of 2933. So that means, any kit that is rated 2933 or higher, will plug and play at 2933mhz. So anything you want to run higher than 2933 will have to be overclocked. Your board supports 3200mzh overclock, so if you want to run at 3200mhz, then get RAM that is rated at 3200mhz and overclock it on your board. It is very easy and will just be a one click in the bios.
Additionally, performance wise, there is not a huge jump going from 3000mhz to 3200mhz. Even less of a jump going above 3200mhz. My suggestion is to get 3000mhz rated RAM or higher.
Also, not sure what your system is for, buy few applications dont require 32gb of RAM. For some workstation task, you may need that RAM. But if your gaming, it is a waste of money. Any unused RAM will just sit idle doing nothing. For 90% of most users, 16gb is more than enough.