Here's the
link with the comparison with other models. Sorry for the order, I have picked the SKU as they appeared on the website. I have added 450 as well.
Some noticeable differences can be that the new X570
* supports more Ryzen generations than B550i.
* has worse DP output than B550i (4096x2304@60 Hz vs 5120x2880@60 Hz).
Does that make sense?
* same RAM (OC) support (up to 5Ghz.).
* has x2 M2 sockets up to PCIe 4.0 (only 5000 series).
Unsure if B550 is x1 PCIe 4.0 and x1 3.0. But it's most likely to be
* Way more/better (IMO) USB frontal connectivity
. This might seem irrelevant, but when you spend +200€ on an ITX case which only comes with USB-C connectors, you wish to have at least one USB-C frontal connector in the mobo so you don't have to remove the connector from the panel. If you can choose, choose to have one. Lately, we expect other devices like monitors to have one.
So x2 M2 PCIe 4.0 and better USB connectivity. I would not dare to say that x570 mobos are better assembled or of much more quality than b550. Neither for the PCB nor the VRMs or anything else. That would defeat economy of scale and Gigabyte is very much into that.