When you bifuricate for example root complex 1 (the top x16 slot) in 4x4x4x4, it is not possible to set it to GEN4 speeds, only the first 4 lanes will get the GEN4 speeds, the others will default to GEN3 speeds, while I've set them all to GEN 4 speeds.
Further when you set the 2 x8 slots to GEN 4, only the first slot will get GEN4 speeds, the other will fall back to GEN 3 speeds.
Also when setting ANY device to GEN 4, the ASPM does not work, you should disable pcie_aspm=off in the linux args. This is in the latest LInux 6.5.5/6.1.55 version.
Any suggestions or advice. I'm also running the latest firmware from your wiki.