U.3 backplanes are incompatible with U.2 disks, so I'll avoid them as good as I can.
I can already see nice problems like "Why does this U.X disk not work?? Oh snap, it's a U.2 disk but the backplane is U.3"
And where did I link those?
Spoiler: I didn't.
It was @wildpig1234 in Post #28 https://forums.servethehome.com/index.php?threads/cheap-asrock-wc621d8a-skylake-cascade-lake-xeon-workstation-boards.42366/page-2#post-401867
EPYC doesn't support Optane DCPMM (which can be nice). Also, even if you take cheap 7302 into account, Platinum CPUs like 8259CL can be found for very little money.
It's a matter of taste - Both have their pros and cons
No need to guess..
show pid and it will happily show you some info, e.g. for an ICX7450-48:
ICX7450-48 Router(config)#show pid
Version Number: 0003
Part Number: 84-1002599-02
Serial Number: CYQ3334L053
Bench test: Passed
Burnin test: Passed
Test Date: 09/01/15
Date of manufacture at CM...
Just be aware that this Board does not have ANY dedicated onboard networking at all. You might be able to do NIC sharing via BMC though.
Although the newest (public) BIOS for EPC621D8A-2T is dated 4/25/2019, so the WC621D8A has a "newer" BIOS.
I know you're good with BIOS tools @RolloZ170...