I've recently installed a x520-da1 in a Windows 10 workstation. Using iperf to connect to a freebsd server i'm getting connection speed of 1.03Gb/s. Using the same Windows workstation I booted a Fedora installation and ran iperf on that and had a connection speed of 9.4Gb/s. It seems the issue here is directly related to Windows 10.
The freebsd server and workstation are directly connected on their own subnet. x520 has (I believe) the latest driver which is 3.10.162.1.
