I tried again with a 440FX chipset and it still worked fine with VirtIO-SCSI and the
virtual NIC.
I also discovered the other reason I prefer VirtIO-SCSI, which is support for discard,
always appreciated by SSDs.
It would seem that the virtio family of storage and network adapters support both PCI and
PCIe incarnations and whoever assembles the final KVM config does it right.
Also cross-checked with FreeBSD 12.2 (instead of GhostBSD) and again the VirtIO-SCSI disk
was not recognized, even if VirtIO support seems to have been added with FreeBSD 11.
I'm afraid that I've exhausted my play-time budget with this, but since I used to
be a fan of BSD (and still love pfSense) it was worth trying.