@cpasmoi - I don't know that there is a specific recommendation here. You really don't need CPU direct interface speeds because the card re-clocks all data going out on the USB connection anyways. I have read that Pink Faun recommends the first slot (the slot farthest away from the CPU). That's where I have my Pink Faun card. Do you have a OCXO clock on the Pink Faun card? You might be space limited here, especially if you have a video card. Otherwise, you can use the HDMI output on the motherboard, but only if you have a embedded integrated graphics AMD processor (the model names end with a "G", such as 3600G).
Be aware that there is a special condition on the non-shielded PCI slot: PCI_E4 will be unavailable when an M.2 SSD is installed in the M2_2 slot.