ethernet speeds

Just to be sure, by "MBPS" do you mean MegaByte or Megabit per second? I'm assuming that you mean the latter ... correct?

Regardless, do you have one of these powerline adapters connected directly to your main Internet router. Since you are attempting to get a pseudo Ethernet connection over your home's electrical circuit between rooms with brick walls ... is the electrical circuit you have both of these adapters on the same circuit. That is, does this electrical circuit terminate at a single breaker? If it doesn't, this could be the reason for the performance drop.

With wifi connection, can you depress and hold the Option key and click on the wifi icon in menu bar and post screenshot of the wifi window that opens. This will give idea of if the observed connection speed is commensurate with the wifi connection parameters.

As a test I would one of the following:

1. Get a long ethernet cable and connect the Mac directly to the router. Alternately you can temporarily move the Mac near the router and use direct ethernet connection.
2. Get a long power extension cord and and try the powerline ethernet with one end of the extension cord plugged in the same ulet at the powerline transmitter and the other in the room with the computer.

1. SInce you have the powerline hardware try using different outlets in the room w/computer and the room w/router
2. Yu said that you two brick walls between computer and router. Maybe get a wifi repeater (or whatever they call one) in the are between the the computer and router.

Those parameters are consistent with mine when I connect to a 2.4 GHz network

But slower than when I connect to ax (wifi6) network

Note that although a 5 GHz connections is theoretically faster than a 2.4 GHz networks, a 2.4 GHz signal is less attenuated (penetrates through walls better) than a 5GHz network

Packets going to the Internet are sent to the TOPMOST, working interface listed in System preferences > Network.

If Ethernet is a possibility for you, move Ethernet to be the TopMost interface. When no cable is connected, it will not also be Working so Wi-Fi (or whatever is second) will be automatically active instead.

Use the gear icon under the list of interfaces and choose "Set Service Order". Then drag Ethernet to the top of the list.

Re: Wi-Fi

Surprising (to me anyway) was the discovery that the Mac Pro 2009 thru 2012 models have only Two Wi-Fi antennas on the stock Wi-Fi card. (Some other Macs have three antennas).

So the 117 transmit speed is next-to-the fastest your Mac and produce on that 2.4GHz band. It uses 64-pattern QAM, the most complex pattern possible, at one-click-back-from-maximum possible speed of 130.

If your Router supported 5GHz band and it had adequate signal levels, your Wi-Fi speed could be about twice as fast.

-63dB signal level is ordinary. Not a problem unless there is a lot of competition or a lot of interference in your "network neighborhood" (for example, it that other network shown was also trying to use channel 1 at the same time)

RE: powerline Ethernet

advertising is very deceptive compared to "real-world" results.

Some slowing occurs when the powerline sending unit and power line receiving unit are on different circuits. The signal travels back to the breaker-box, through the branch circuit breaker, along the Bus bars, through the other circuit breaker, and out to the other device.

The most slowing occurs when you are using two circuits that are on apposite phases in two phase power. But in Australia, I don't know whether two phase power is even used.