Erlang processing is slower than C by quite a bit but the reduced threading costs tends to make up for it when you are in a scenario where you need to serve multiple requests simultaneously.

On an apples to apples comparison well written C is going to beat erlang on this every time but once you start getting into threading, mutex locks etc. the equation starts to shift more towards Erlang favor _as long_ as each request you are serving is not highly computational in nature and would involve semaphores, and so on for thread management in c.