The b550 Aorus Master I just got is unique in its bifurcation. It maps the CPU's gen 4 PCI-E to the main 16x slot and one M.2 4x, or drops the 16x slot down to

The b550 Aorus Master I just got is unique in its bifurcation. It maps the CPU's gen 4 PCI-E to the main 16x slot and one M.2 4x, or drops the 16x slot down to 8x and then has three gen 4 M.2 4x. The other two PCI-E slots are gen 3 through the b550 chipset. I chose this board for its absurdly overkill CPU voltage regulation. The pci-e configuration seems like a pretty good compromise, though.