If I was going to buy an x570, wouldn't it make sense to buy the best memory that I could afford? Like DDR4 4000 - DDR4 4800. Especially if I invested in a premium board already.
Or, maybe a high spec x470, but tbh, the x570 are probably better in most ways and cost a similar amount. I think they could be more future proof too.
I bought some Patriot viper steel 4400 CL19 seeing as the reviewers got 3600 CL16 @1.35v. At the time (couple months back) is was going for around £160 2x8gb