5.0.3 seems to date back to 2005-03-23. Although there aren't a huge amount of new features, there are things like 5.7 introduced an ALTER TABLE syntax to rename indexes
5.7.1 dates back to 2013-04-23, so maybe "too new"...
5.6.2 dates back to 2011-04-11, Developer Milestone
We're supporting PHP 5.5.9, which is from 06 Feb 2014 http://www.php.net/ChangeLog-5.php#5.5.9 so maybe 5.7 is alright, and isn't too new?
The 1.30 development cycle has started, so now would seem a reasonable time to be upgrading, giving time for it to settle etc as necessary