Wordpress - Extremely Slow on Large Site - get_page_children Function Responsible

I'm converting a large information site from HTML to Wordpress.  There are over 10,000 pages of content.  On some themes the site crawls, on basic themes like TWENTY TWELVE it flies.

What I have isolated is a function function in post.php that is causing the slow down.  

/**

COMMENTED OUT BY ME

function get_page_children($page_id, $pages) {
     $page_list = array();
     foreach ( (array) $pages as $page ) {
          if ( $page->post_parent == $page_id ) {
               $page_list[] = $page;
               if ( $children = get_page_children($page->ID, $pages) )
                    $page_list = array_merge($page_list, $children);
          }
     }
     return $page_list;
}
*/

/**
Added by ME
*/

function get_page_children($page_id, $pages) {
     $page_list = array();
     return $page_list;
}

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Basically, it seemed to be doing a tremendous number of recursive searches over 10,000+ pages looking for matches.

Is there a more efficient way to do this with a SQL query and, if yes, what would you do?

This has been a temporary fix.... the site is now flying.  The Parent / Child plugins we use do not make use of this function.

The only thing I've seen it break is:

http://www.XXXXXXXXXXXXXXX.com/wp-admin/edit.php?post_type=page

This would list all pages on the site that we could edit, albeit at 20 pages per screen.

Other than that, is this a problem?  Is there a better way to do it?  I know sites this size are unusual but should not be impossible.  

I know this is well established code in WP, but it cannot be the most efficient way of handling things when dealing with a large site.

Finally, is there any way for me to take whatever function is recommended and make it a child theme / function / something that "takes priority" over the one built into post.php?

I can edit post.php but if we do a WP update, it will wipe the change.  I'm wondering if you can have priority functions, the way you would take precedence in CSS.

Thanks!