I have it currently running correctly on a PCI 2.0 1x slot on a asus motherboard (z170-deluxe).
When placing it in the PCI 3.0 slot i had wierd game lag.
when i tried that i noticed that my GPU PCI-E dropped from x16 to x8. This might be motherboard specific but its something you can see with gpu-z. When mine was running on x8 doom vfr went all stuttery on me.