are you dead set on B550 boards? on these high end B550 you get better value from X570 if you can put aside the the whole chipset fan business.
for instance MSI Unify as an example
X570 - 3xM.2 onboard all PCIe4x4 and can be populated wihtout affecting the primary PCIe4X16 for GPU. you got an additinal PCIex16 @ PCIe3x4 for addon cards etc. SATA drives are not bandwidth shared with any of the above.
B550 - 4xM.2 onboard. but only 1 will run at full PCIe4x4 while another will run at full PCIe3x4. the other 2 will run at PCIe3x2 speeds but you start to loose SATA. otherwise if you want all 4 drives to be at full x4 then you loose GPU x16.
the major difference between B550 and X570 is the amount of PCIe lanes available through chipset. B550 is all PCIe3 and has to share resources with SATA also. where X570 you have more lanes and your get the PCIe4