Ubuntu 18.04 VFIO GPU passthrough with a single GPU (onboard automatically disables itself)

Hardware

https://www.reddit.com/r/JDM_WAAAT/comments/8zgkfj/server_build_nas_killer_v_20_the_terminator_dual/ 2x X5650 from this thread Aside from that build guide, a generic USB3 card and an AMD R9-200

Grub

Modify /etc/default/grub and add vfio-pci.ids=dead:beef video=efifb:off to GRUB_CMDLINE_LINUX_DEFAULT (use the PCI vid/pid of your primary GPU, not dead:beef)