Has anyone run similar tests on the soon-to-be-released PHP 5.4? From what I understand, one of the changes in that release is reduced memory consumption. Andi Gutmans has said that PHP 5.4 could lower PHP's memory footprint by as much as 35%.
I actually did most of my tests with PHP 5.4 and trunk binaries, but also tested PHP 5.3 and the numbers didn't change. PHP 5.2 used 8 bytes less, because the circular GC was introduced only in PHP 5.3.
By the way, you can test that yourself too. The codepad I posted the same on has a switch for PHP 5.2, 5.3 and 5.4, so you can easily see for yourself :)