A custom Drupal development company, 2bits, decided to do a performance comparison of Drupal running on Zend Server CE vs. Apache mod_fcgid. (They had previously done a comparison between mod_fcgid and mod_php)

Since [Zend] a) offered DEB packages, b) supported Ubuntu Server, and c) had a zero cost community edition, there was no hesitation on our part to give it a road test and see how it compares to the free/open source alternatives. Zend’s Optimizer has been long known to offer really good performance. So, we decided to benchmark Zend Server Community edition with Drupal 5.x against Apache PHP fcgid with APC, which we have benchmarked recently.