factors that determine socket.io+node.js emits

I have a node.js+socket.io server for sending messages. As it is not multithreaded, and handles one request at a time, i wanted to know what factors can make the emits faster?

I create a simple test server which only sends strings across sockets.

If i keep sending messages rapidly between only two users(like 1000 in a minute), the socket.io+node.js server gets extremely slow and messages start getting delayed by minutes. So what all can i do to make this faster? Also, does this effect the node.js server handling the messages or all node.js servers? If a create two server for handling messages will the performance get better?

Use Redis as your state store (see https://www.npmjs.org/package/socket.io-redis) and scale out (deploy to multiple servers and use a WebSockets aware load balancer). Yes, performance will get better.