I guess I was not thinking so much as performance, but rather good structuring and coding.
I think I might have come to a little bit of a workaround.
I'll simply create a php file called 'classes.php'. Then, within classes.php I'll have the following:
include('user_class.php');
include('contact_class.php');
include('project_class.php');
etc.
Kind of like 'packages' but only in an organizational sense.