C7100V - why is *wired* ethernet so slow

I have a C7100V whose wired ethernet connections choke internet traffic at 60mpbs or just over 100 on a good day. 

• All devices I have tested are gigabit ethernet capable. I've also tried USB 3 to ethernet adapters on the same machines.
• On wireless and internet, I get up to 300 down via 5g wireless an entire floor away, so it's not my internet connection.
• I have tried both cat 5e and cat 6 cables.
• Netgear is set to port speed Auto (I also tried forcing 1gbps).
• Windows networking drivers have been reloaded.
• Windows machines read 1.0 gbps as the connection speed.

Has anyone else experienced this? What am I missing here? I am trying to test the actual internet speed of the C7100v (which should be over 400 with xfinity).

Previously, I had thought that Netgear AV2000 powerline adapters were slow (maxing around 50-60); but now I am seeing the same speeds with those disconnected and the computer plugged right into the C7100v.

And it's pretty abnormal for a hard line to lag significantly behind wireless connections.

Thanks,