socket.io impact on ubuntu server performance

I have tried several times to scale my chat application with socket.io. I hit some kind of wall when trying to establish more than 2k web-socket connections on the same machine. This number seems a bit low considering that my local machine is a 8 core 6 gb of rams and during test only half the ram and the CPU is used. Being a nob to web-socket and Linux i might have not configured my server perfectly so far i raised max number of open files to 500000 and max number of open socket (maxconn) to 60000 with no effect.

So my questions are:-

1. How this will impact server performance?
2. How much more requests/sec this will cause on my server?
3. Is there a limit in the number of connections that can be created locally using socket.io?
4. How many concurrent connection have you been able to establish on a single machine using this kind of setup?
5. Are there any other Linux settings to tweak in order to improve performance?

Currently, I am using Ubuntu 18.04 and my application in node.js.

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