Why would I go for a X470 when the X570 supports higher speed RAM and PCI-e 4.0 could be interesting for future graphics cards?
The CPU has the memory controller, not the mobo. Look at some reviews, i.e. - https://www.overclock3d.net/reviews/cpu_mainboard/amd_ryzen_7_3700x_ryzen_9_3900x_x470_vs_x570_review/7
On x470 max RAM speed of 4200MHz, on X570 - 4600MHz. I bet you are not plannin to get RAM anywhere near 4000, so the argument is pointless.
PCI-e 4.0 is irrelevant for GPUs and will be irrelevant for the next two gens at the very least (by that time PCI-e 5.0 will be out).
Plus the fans on x570 mobos are loud as ****.