I just recently was in this same situation (deciding whether to serve static via express' static middleware or nginx), and nginx proved to be a better choice -

I just recently was in this same situation (deciding whether to serve static via express' static middleware or nginx), and nginx proved to be a better choice - the response (on a non-loaded server) was faster, and less server CPU time was used up. Wasn't a scientific test, but the results were consistent enough for us to decide to use nginx. (FWIW, neither nginx nor node did SSL termination - we have haproxy in front of them taking care of that and the load balancing itself).