I’ve got a lot of experience in this context re: load testing web servers, apps, systems & networks and this page gives some good info on it:
http://www.mnot.net/blog/2011/05/18/http_benchmark_rules
It’s good that it mentions a useful tool that I’ve also used in the past too, being ‘siege’ (available as a standard package in Debian Linux for example via: apt-get install siege)
There’s also some great contributions in the Comments of the above site too..