My Mac mini is connected to my router/modem by Ethernet. I want to know how fast the connection speed is between the Mac and the router.
Obviously, I can use a website like Speedtest.net to get my Internet connection speed, but that doesn't tell me whether the Ethernet connection is a limiting factor, or how much 'spare' capacity there is for local traffic.
The mini serves to other devices. The Ethernet is over a powerline, and the cables are ancient, so may not be optimal.
If I were using Wi-Fi, then the data throughput is shown by holding Alt and clicking on the Wi-Fi menulet icon.