I have a question - does anyone has any benchmark data re. using Express JS framework vs pure Node.js?
Is this something that even should be considered -- or using Express or similar framework is definitely a MUST if you're building a more or less large web app?
EDIT:
The article I linked to below disappeared, and I couldn't find it after searching around a bit. However, in lieu of that, here are a couple of relevant references with sufficiently scientific benchmarks:
Although this doesn't answer the delta part of your question, there's some absolute statistics about ExpressJS performance here:
http://blog.perfectapi.com/2012/benchmarking-apis-using-perfectapi-vs-express.js-vs-restify.js/
Looks like, on a small Amazon instance, Express averages:
a very respectable 1,600-1,700 requests per second
Express is a convenience wrapper around node.js, and should not add much latency to your server; your code would probably go through many of the same steps anyway. That being said, if your load tests (or hapless customers) find the server is too slow and/or not scalable, then you should profile at that time, and the bottleneck probably won't be Express.
BTW, even though Express calls itself "high performance", they're naughty for not posting measurements.