I got a work call halfway into reading your update and got sidetracked. I didn't finish reading you post before replying.
Virt was turned off first thing so no. I'm going to re-enable it and add the blank .conf. I'll monitor the logs for the rest of the day.
You can add : Dell R730xd to that list.
It uses (in my case at least) the Broadcom 5720-T 4 port NIC with the tg3 driver.
As a preventative measure, I've disabled virtualisation. I'll run my VMs on a temporary proxmox machine.