As per this reply from support.

Please advise what my best options are to ramp up speed across my house:

https://community.tp-link.com/en/home/forum/topic/622572?replyId=1252896

I've now upgraded to 900 mbps Fibre connection to the house. Satellite Deco's are still running at 250 mbps. Everything on cat 6.

I need to test my mac against the router and also the main Deco unit via ethernet.

Upstairs via wifi to the main router downstairs i get 602 down 682 up, via wifi to the main deco downstairs 180 down 396 up