1) Add a raw http test -- no template compilation or html, just return "OK". Would give a relative idea of the cost to "just turn the thing on"
2) Don't json encode after the database tests. By json encoding you're doing two things but saying you're only testing one.
I come from the python/django world, and I know that different python json packages have orders of magnitude differences in their performance. From that I can infer that there are probably similar or greater cross-language differences -- I suspect node.js having json as a native object type helps immensely.