I get above 300Mbps download speed with my Asus router on wifi, upload is slow as always with Shaw (~25Mbps...) same as wired. RT-AC86U and also using RT-AC68U in AiMesh configuration.
I've never used a Shaw cable modem as wifi router, always set immediately to Bridge Mode, with the new XB6 you can enable Bridge mode yourself in the config. screen of the modem what is nice.
I think you may have more issues going on than you realize..
If you plug in hardwire and it drops to 90 mbps I am thinking the network port on your device (or the cable) is only 100 mbps. If wireless and you are max at 120, I suspect the WiFi card in your device might be old and be N only. If the hardware LAN is only 100 mbps then I suspect the WiFi card is older too.
As for the router, personally I'd use the Asus AC3200 just to maintain control over your local network..
I go the Dual Band Wireless-AC 7265 on my laptop...not sure if that needs to be updated?
Also tested the connection on my Xbox one X wired and wireless its hits <100 Mbps.
Just strange that before I had the 150 plan i was hitting 177 Mbps wireless on this laptop now I'm hitting 90's on 300 plan.
When I did call Shaw constantly why I was getting 30 on my 100 plan for years one IT support guy said it had nothing to do with me it was some types of 'Nodes'(?) that Shaw needs to update in my area.
Is there a way to test if I am able to get faster speeds? other than speedtest online?
I think the moral of the story is that you you are getting less with the 300MBPS plan. I am experiencing the same issues with the 150 that I just had installed, I got more with the 75 plan than the 150 plan. Can it be the XB6 modem?????????? I had the Hitron with the 75 Plan.
Who knows, I am waiting on an open tech support "ticket" to look at the issue. I think that I will probably drop back to the 75 Plan as I got better overall speeds throughout the house with that plan. I used to get 75 MBPS on at least 2 deices and and at least 30 on another tablet. Now I get 150 on one device and 35 on the other.
This is an outside your house issue, NOT inside, Shaw just isn't pushing enough bandwidth into your house.
Something like iperf between devices on your LAN will prove out your hardware. But it isn't 'simple' to use.
Otherwise if there are node issues, you're not going to be able to do anything to fix that..