Neither board seems to offer PCIE bifurcation so the x16 slots are fixed. In this case, X670 one does offer more usable PCIE lanes, so you have to decide depending on your need of PCIE devices and M.2 devices throughout the board's lifespan. The other notable differences are audio and LAN: X670 with ALC S1220A and Realtek 2.5 Gbe, B650 with ALC 4080 and Intel 2.5 Gbe. I think they are a wash, so it again comes down to PCIE and M.2.