@stephenw10
The ping test could have been after ARP expiration.
Once the network failures were history, I tried switching to VirtIO, but speed was 35M even with offloading disabled. I set it back to Bridged, and got 250M with 4 CPUs. 2 CPUs in Virtualbox gave me over 500M. Not bad, but still ~50%.
Each reboot I would lose connectivity on the i211 LAN and the only way I could get it to work was to switch it promiscuous mode on/off while the VM was running. Crap...
I gave up on Virtualbox and moved it over to Hyper-V with 8 CPUs set. I got 30M, researched, and disabled RSC (even though it was already reported as disabled) via PowerShell with these commands:
netsh int tcp set global rsc=disabled
Get-NetAdapterRsc | Disable-NetAdapterRsc
Then I could get a solid 940M in Hyper-V, AND have the luxury of auto-start after host reboot. (Lessons for anyone reading this)