Socket.IO is extremely fast, I have used it to update a wall display hundreds of miles away from the computer generating the graphics.
I remember in the 90's being able to chat with people using modems. Each character you typed was transmitted and displayed on the other person's screen. You could see how fast they type, watch as they corrected mistakes, etc. I would love to see if Socket.IO could be fast enough to accomplish this. In fact, I might just give it a try.