Last week, I connected my 8-wired "phone cable" of unknown quality to two CAT6 Ethernet wall plugs. The OS then claimed I now have Gigabit Ethernet.
Today I tried to verify this using netcat (see first comment). I connected my PC an Laptop to the router and started on the laptop:
nc -l -p 44444 > /dev/null
and on my PC:
yes | pv | nc serverhostname.example.com 44444
Here is the result: