I’m new to all the PCIE4 , I recently purchased Asus Strix B550-I for this build , I’m assuming I shouldn’t get a Gen4 SSD if I’m not getting gen4 riser at first as it wont be running full speed , as I’m assuming the front gen4 m.2 slot and the PCIe slot are both affected selecting Gen3 or Gen4 mode?
I think the PCIex16 slot (for display card) and the M.2_1 (for SSD) both receive their PCIe 4.0 lanes from the CPU (ie not from the chipset B550).
And, the Asus B550I BIOS manual seems to suggest that both can be independently adjusted regarding the link mode. I suppose, [Auto] is Gen4 for the PCIEX16 and M.2_1 Link Modes.
The PCIe signals for each come from different PCIe root complexes on the SoC (I've never seen a PCIe root complex providing more than 16 lanes), so the only reason their link speeds would be matched would be if a manufacturer took a shortcut in setting up their BIOS. Which is of course possible, but at least on paper these should be individually adjustable like in the Asus BIOS above.