Dries Buytaert has written an article in which he compares various server configurations in regard to Drupal performance. His benchmarks cover APC (Alternative PHP cache) or no APC, PHP4 or PHP5, reverse proxy, mod_php or FastCGI, Apache or LightTPD. He concludes that:

the slowest configuration is Apache 2 running PHP5 as an Apache module without using APC. Unfortunately, this is one of the most common configurations. The fastest configuration using the more secure FastCGI method, on the other hand, is Lighttpd with PHP4 in FastCGI mode using APC. For anonymous visitors, the latter is almost 4 times faster than the former, while being more secure.

Drupal webserver configurations compared