Was trying to find benchmarks comparing the alpha versions of PHP 5.6 to 5.5, and I couldn't find any, so I ran some myself. Nothing really crazy to call home about... In my benchmarking tests PHP 5.6.0 alpha 2 is ~3.5% faster than 5.5.9. Used the standard bench.php and micro_bench.php benchmarking scripts.
this might be because you are using php with apc built in, and as per my understanding, php 5.6 has apc built in , as compared to php 5.5 < which require apc to be added as a module.
ok ,my bad, i had old info, apc is now dead. ( for practical purposes, future compatibility) http://wordpress.org/support/topic/looking-ahead-to-php-55-zend-optimizer-the-end-of-apc?replies=21