For some real-world(ish) benchmarks, see : http://news.php.net/php.internals/57760 http://news.php.net/php.internals/57760 Memory usage is the big winner, e.g.

For some real-world(ish) benchmarks, see : http://news.php.net/php.internals/57760 http://news.php.net/php.internals/57760 Memory usage is the big winner, e.g. a 50% improvement for Drupal, with performance in terms of requests per second being lower (e.g. 7% for Drupal) but still an improvement. And memory improvements can lead to greater performance improvements when scaling out or on overloaded hardware. Just to note, this was back in February in a pre-release version of 5.4, and things have improved in a couple of areas since then.