Rob Allen has shared some of his personal experience in how much faster PHP 5.3 is over the latest version in the PHP 5.2.x series when he tried to change up some view helpers in his Zend Framework application.
I was looking at the way view helpers work in ZF2 and thought it would be more convenient if we altered the syntax a little. A side-effect of the change was that we'd have to use call_user_func_array, which is perceived as slow. I thought I'd whip up a simple test to find out how much slower it would be over a direct method call.
He includes the sample code he used to benchmark the request times between the two versions measured by microtime. In his results he saw a difference of almost five seconds between the same code running on 5.3 versus 5.2 (according to test runs on his laptop).