"It's likely your Cat5 cable. Cat5 maxes out at 100 Mbps. You'll need at least a Cat5e."
Yes, that's why I mentioned it in post 7 above.
The ethernet cable was installed back around 2009/2010 or so. Back then I was on ATT DSL which maxed out at about 4mbps if that fast.
My sister (who had never had a computer before) got a Dell "Mini 10" laptop which I put a copy of the Mac OS onto (wasn't really that hard). It was clunky, but it worked (later she got a white Macbook, still using it).
But... I didn't have a wireless router -- just an old Belkin wired router.
So... I just bought a long ethernet cable and routed it from the second floor (where the DSL modem was), over the doors, down the staircase, to the ground floor. She could plug into the ethernet and "be on the net". What works... works. Her friend later gave us an older Airport Extreme, and that worked quite well for a while.
Later, we were able to upgrade to ATT Uverse (tv/phone/net), and the ATT gateway was relocated to the ground floor. So I just used the cat5 ethernet to "send the signal in reverse" back upstairs.
Eventually, I got a Linksys Velop. It worked well enough, but with Uverse we were still only getting 8.4mbps at best.
Frontier took over here from ATT, and their prices skyrocketed, so I finally moved over to Comcast cable. The install guy ran a test with his equipment and found the cable line good for around 500mbps (even though I was only paying for around 170-200).
He said the speeds he got were only available using the test equipment he had, not for regular subscribers. So I was surprised when I was able to show 450+mbps using the "SpeedTest" app (free download from the App Store).
I can only get that using a wifi connection, however.
The old cat5 cable can't handle it.
I tried a speedtest upstairs (2012 Mac Mini) while he was here, and was only getting 95mbps or so. He said it was probably due to the old ethernet cabling.
So... there ARE examples where one can get MUCH faster speeds using wifi rather than ethernet!