Currently on a 1Gbps Unifi plan.

Modem : white Unifi modem. not sure of the brand. I also have the Skyworth modem/router.
Router : Asus AX4200 as main
Node : Asus AC86U upstairs

PC upstairs connected to AC86U wired

Currently, I'm able to get 700Mbps downstairs but only about 170Mbps upstairs where I have most devices. I am able to get 1Gbps using the Skyworth combo but upstairs is just bad. How do I improve the speed upstairs? I am considering Deco X20, X60, BE65 or even Asus XT8 or any suggestions.