@Pianophile 

Well, do you have AC or AX wireless devices? Need those to probably go over 300Mbps.

Also, on the devices, FORGET the network and re-connect as new. Usually helps.

@IrvSp 

> Well, do you have AC or AX wireless devices? Need those to probably go over 300Mbps.

Yes, my iMac is my primary device, and it is connected ot the router via 802.11ac, usually at a Tx rate of 700-800Mbps. 

> Also, on the devices, FORGET the network and re-connect as new. Usually helps.

I removed and re-added my preferred network, and all I get is 284/169 up/down. 

@Pianophile 

> I removed and re-added my preferred network, and all I get is 284/169 up/down. 

Following a tip I found elsewhere on the net, I reset the AX6000 to factory specs, and set it up again, including some saved settings, but none related to wifi config. Now, when I look under QoS for example, I see 490/538 up/down, which is a lot closer to what it should be. Not sure how I could have gotten that to refresh without a router reset.

On my iMac, which connects over 802.11ac, I am seeing 343/362, which is now above 300Mbps, though still low. On my laptop, which can connect over 801.11ax, I see 369/555, which is weird, but a little closer to what I'd like to see. 

At this point remining oddities aren't at the router level, though, so I will try device-level tweaking from here.

Thanks for the reply.

@Pianophile 

Well, there are AC and AX devices, and not all are equal?

I've got 2 PC's here with 400/20Mbps ISP service, both wireless or wired connections. One PC has an AC 1300 device, the other an AC 1200 device.

Here is some data from my AC1300 device:

Two things to note on the USB attached device, the Connection/Data Rate and the USB versions.

I get 480/23Mbps Down/Up. That is because the ISP over-provisions the speed by 20% or more so they do not dip below the advertised rate (I'm on Cable).

Don't know the actual CHIPSET on the Mac's, but if you don't have the latest (check chip maker's site) you probably can't connect the fastest. I had older drivers and had less speed. Note it states USB 2.0... and that would limit me to a lot less speed. Fortunately, the chipset on the device will switch to USB 3.0 as needed. Max. at USB 2.0 would be 480Mbps anyway, USB 3.0 is faster, GB capable, but I can't go any faster anyway. Yes, depending on what is happening during boot, I will see the Mode as USB 3.0 most of the time, but speed never changes.

So, look to ensure you have the latest drives, I'm on Windows, not sure how you can do that on a Mac? Look at the SECURITY and ENCRYPTION and also the CHANNEL and WIDTH. Using WIDE width will provide more speed.

Depending on when the AX device was made, and specific router's, some don't perform as well as other combinations.

You might find these 2 web pages and interesting read to help understand more why some speeds are what they are:

https://www.duckware.com/tech/wifi-in-the-us.html

https://www.duckware.com/tech/wifi-in-the-us.html#PHY

@IrvSp 

Thanks for your reply. So far via terminal commands I am able to see that my (2017) iMac has a Broadcom BCM43602 wifi chipset. I suppose it's possible that the speeds I'm seeing are as fast as I can get, but I wonder. I't's good to know the router doesn't appear to be the culprit, and I will pursue further in a macOS forum.

Thanks!