Benchmarks are extremely important when making infrastructure and configuration changes. The Raspberry Pi is by no means a 'high performance' computer, but even with it's power-starved architecture, we can optimize many different parts of the stack to make the Pi perform well.
But benchmarks are only helpful if you're testing simple changes in isolation, and if you can compose different benchmark results to find ideal performance and availability scenarios.
This section of the wiki explores benchmarks on the hardware level (e.g. disk access) all the way up to tweaks to PHP and Drupal itself to make things faster.