@LeVeau 

Remember that a speed test is between two different points. You are only as fast as the slowest link.

Not sure which host (city) the router connects to to get the speed.

I always use the ISPs speed test or one of the internet based speed tests and run it from my device to a more accurate test. 

Also, you need to check to see if you are using IPv6 or IPv4. For me, IPv4 gives me slower speed.

@ArcherC8 

The test, which is built into the router's firmware, tests through the cable modem. It doesn't indicate where the test server is located.

The MacBook Pro test involves removing the cable from the router and plugging it into the laptop. There, I use the Speedtest.net site, and the test is to Comcast in Houston, although other nearby servers are sometimes selected. 

The built-in test also uses Ookla Speedtest.net, so I am assuming it's going to the same server, but there's no indicator. I may just have to abandon the internal router test, but it's sure a lot more convenient than unplugging the modem from it, restarting the modem and waiting for it to resync before testing on the MacBook Pro. Looking for a solution in settings or whatnot.

@LeVeau 

The only time I disconnect the router from the modem to do a speed test is to check the difference between the PC-modem vs PC-Router-modem to see the impact of the router.  I have found very little difference in the two speed checks.

It would be great if the router's speed test gave you more info and the option to select the host city so you can compare the two better.

I have Xfinity also but only 200 service and get in the 230s most of the time.

Are you using IPv6?

Also what is the hardware network limits of your PC? Look at your hardware network settings in the Ethernet advance section of your System Preferences.

  @LeVeau You are correct, the speed test in the x6000 series is horribly inaccurate and that silly car race game is an insult.  My kids are not the ones doing the test!!!

I have a mix if X90 and X60, when the X60 was primary, it had a nice test and it was very close.  The X90, not even in the ballpark!  It routinely says "not connected" and shows a speed that is not unlike the speed I'd expect from those old modems, remember 1200 baud?

Side-by side, the X90 built-in test and speedtest.net, there is no comparison, speedtest is smoking, X90 is NOT EVEN CLOSE!

Example: car speed test, always 0/0, network test 300/5, speedtest.net 940/900.

TP-Link, please for this!