Gregory McGarry has published an article that benchmarks NetBSD 2.0 and FreeBSD 5.3 in multiple situations that can be of interest in production servers. This includes scalability, reliability and performance in areas such as sockets, threads, process creation...
What's impressive is that NetBSD 2.0 outperforms FreeBSD 5.3 in almost all tests! Moreover, the areas in which it doesn't are not very important when it comes to real production servers. For example, the test that measures thread creation times doesn't reflect reality, because real servers won't manage that many threads. Anyway, it shows areas that are worth optimizing.
Now read the article and check it with your own eyes ;-)
Edit (Jan 7th, 21:24): Added missing link to the article (see above).