I have a test before to compare the performance of PHP 5.5 and PHP 5.3. The result is PHP 5.5 is 20% faster.
Now, I replaced PHP 5.3.3 by PHP 5.5.3 at this server, which my blog is on.
The php -v information shown as below:
PHP 5.5.3 (cli) (built: Aug 24 2013 10:14:23)
Copyright (c) 1997-2013 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2013 Zend Technologies
with Zend OPcache v7.0.3-dev, Copyright (c) 1999-2013, by Zend Technologies
I followed the instruction of webtatic to install PHP 5.5
Based on my subjective experience, it is more than 20% faster. Maybe not that much, but it did faster.