If you want dynamically typed plus speed, your options are not great on Unix right now. Straight Ruby, Python, and Perl do not really cut it. You could try JRuby or Jython to see if the JVM speed for Java has rubbed off on them, but that requires diving into the complexity swamp of the JVM and those implementations are somewhat second class citizens of those languages. Otherwise, for real speed you are looking at a statically typed compiled language: Java, C/C++, maybe Go.
PS: If you look really hard there is probably another dynamically typed language that runs on Unix and does so as fast as node.js (I suspect that there are some Lisp implementations that are in the same ballpark). But I don't think there will be anything that's anywhere near as well known or popular as node.js. And frankly that makes node.js a much safer choice.