@coliver I have read that a lot of NIC drivers do the VMQ implementation poorly in drivers which can kill performance, so I usually disable it, just to be safe. Most notably, this problem is especially prevalent on the Broadcom chipsets... I see you have intel.
It may be worth a shot, but there will be a brief blip if you use the powershell command to disable VMQ.
get-help VMQ
will list the commands.
get-netadaptervmq|where {$_.Name -eq 'NIC1'}|disable-netadaptervmq
Just replace NIC1 with whichever NIC is currently running your PBX VM.