So, there are no real benchmarks of a Wordpress running in the wild available ( couldn't believe it either.. ). So I got my ab and gnuplot friends and created one. The reason why I'm doing this that while developing ( or forking, to be honest, marc's work ) i was curious what php can achieve. The answer is, as you will see, very sad.
I ran the benchmarks on two different machines. One of them is a xen-based virtual machine with 4gb of RAM and a dedicated CPU. The MySQL server runs on a seperate VM on the same physical device. The first graph shows the results at a concurrency level of 2, the second one a concurrency level of 5.
The second run was performed on the machine where this blog is hosted. All benchmarks are running against Wordpress' index.php, to not allow caching to falsify the results. The machine is also a virtual machine, enough RAM, slow cpu though. Please keep in mind that most people are using that kind of machines for their blogging, because dedicated machines are not exactly.. cheap. Anyhow, concurrency level 2. I didn't bother to check what level 5 would have changed, because the time taken for the first one was already 20 minutes.
For the sake of being mean to all PHP-lovers, I included a bench of an Rails-Application served from the very same VM as the first benchmarks. Of course, you can't compare Rails to PHP. But still interesting, I think.