I'm actually of the thought that k-series CPUs are just regular CPUs with a non-working IOMMU, so instead of throwing it out they unlock the multiplier and sell it as an unlocked CPU.

Binning is a hell of a thing.

Though from the research I did, unless you're running a Type 1 hypervisor vt-d is not necessary (or usable). Type 2 hypervisors will use vt-x only.

What are your sources for that? VirtualBox seems to fall under "type 2", but supports PCI passthrough using VT-d on linux hosts.

About 10 hours of crawling through forums, VMWare documentation and a couple of conversations with people about ESXi. So all of it pretty unreliable ;)

I'd love to see sources/evidence to the contrary.

IOMMU is needed for VGA and PCI passtrough in general.

VT-d is still useful without any hypervisor, to guard against DMA attacks by malicious connected devices.