I would only enable ECN if your router/modem support it, and in the presence of packet loss. I am pretty sure Asus routers support it, not sure about your modem. Chances are you wont see much difference.
Other than that our gaming recommendations are listed here: https://www.speedguide.net/articles/gaming-tweaks-5812
It may also be good idea to study where the latency starts to occur, on which hop between you and the game servers (you can use a traceroute for that). I would also look into reducing any possible bad effects of interference in your location, as in keep the modem, router and Ethernet cables away from possible sources of EMI (including keeping the router and modem at least a foot apart, they're often not shielded well).
It is quite normal to have considerable increase in latency when you are close to your line's bandwidth limit, you may want to reduce the streaming quality/bandwidth to combat that.
I hope this helps.
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