I come across this question on benchmarking WordPress in almost every optimization project I work with. So, here is a quick post to make the answer available to everyone (who might ask this question in the future).
Benchmarking can be done in two areas. Firstly the server benchmarking. It is the ability of the server to manage N number of concurrent visitors to the site. The other is application (WordPress) benchmarking. It depends on how quickly it can generate a complete webpage for the server to serve the visitor.
