X16 PCIe slots available for connection
X16 PCIe slots available for connection
The motherboard details explain the PCIe connections. The ASUS B350 Prime Plus uses an X16 slot for PCIe x16, and the second PCIe slot is managed by the chipset. This means the second slot can only support x4 bandwidth with a GPU installed (like Crossfire) if it's configured properly. You mentioned not having M.2, so that part isn't relevant here.
The shared graph appears to represent IRP rather than bandwidth. It's restricted to x4 from the chipset, so avoid using this board for multigpu applications.
The first PCIe x16 port operates at full x16 speed, accessing lanes directly from your CPU. The second PCIe x16 port draws from the chipset and can support up to x4 lanes. Sharing bandwidth with the PCIe x1 slots means connecting a card there reduces the second x16 slot's performance. It also varies by CPU; with an Athlon processor, the first x16 slot is capped at x8.
I realized I shouldn't be here since someone mentioned it before, but now I understand. It would overload the lanes on the second GPU when active. A Fury X is coming soon—looks like I can only handle this on my B450 or FX setup.
Using two GPUs at once and consistently getting boards that support x8/x8 instead of the confusing x16/x4 options.
He just looked at that ASRock board; it seems this is where they're heading. My old ASUS FX board might be the next step!