Slow NFS

[DBMandrake]

Might be unrelated but it has just occurred that this may help, can you give it a try ?

Bad video performance on Pi 3

Is your Cisco switch a managed switch ? (EG has a web interface or configuration utility) If so check to see if flow control is enabled on the ports. If not try enabling it. Alternatively try adding smsc95xx.turbo_mode=Y to the end of the line in /boot/cmdline.txt then rebooting.