From what my novice eye can tell, the main difference between the high end x570 chipset and the mid-tier b550 chipset is that the former can use PCIe 4.0
My question is does this make a huge difference? I'm not sure how important this feature is to a motherboard I would buy since I am not sure what hardware actually needs a 4th gen pcie

Only amd has a server side pci 4 gpu.
but they will be coming, just no real info as to when.

ram speed support I think is the main diff.

currently no but if your budget permit it go x570
Im sure bunch of stuff will run on gen4 in a near future