Hello @Alpha5858
1. RE605X supports WiFi6 , 80Mhz. 5Ghz Wi-Fi spec is 1201Mbps=2*600Mbpps when works at 2 MIMO, 80Mhz,802.11ax. So RE could utilize the GX90 Router 5Ghz-1(80Mhz*2 MIMO) and get its highest Link speed at 1201Mbps.
Archer GX90 spec: https://www.tp-link.com/home-networking/wifi-router/archer-gx90/#specifications
RE605X spec: https://www.tp-link.com/home-networking/range-extender/re605x/#specifications
2. As far as I know, Tri-band router 5Ghz-2 (160Mhz) is not included in the OneMesh yet, probably that will be added when 160Mhz RE model comes out.
To fully utilize the GX90 5Ghz-2 gaming-band on certain device, you may consider a very powerful Wi-Fi adapter which supports 4 MIMO WiFi6, 160Mhz.