better AES implementation available

I notice that you're using the AES implementation from http://www.movable-type.co.uk/scripts/aes-php.html. There's a far faster one available here:

phpseclib.sourceforge.net/

It's about five times faster than the implementation you're using, per this:

phpseclib.sourceforge.net/documenta ...

And that's when mcrypt isn't available. When it is available, my own benchmarking suggests that it's more than twenty times as fast. And fast means it's less of a resource hog.