Exclude all pages except a few?

try

   ...
   echo preg_replace('/<ul>/', '<ul class="sf-menu">', 
       wp_page_menu(
         array(
          'include' => '11,13,7,9,4',
          'sort_column' => 'menu_order',
          'echo' => 0)), 1);

or

  ...
   echo preg_replace('/<ul>/', '<ul class="sf-menu">', 
       wp_page_menu(
         array(
          'include' => array(11,13,7,9,4),
          'sort_column' => 'menu_order',
          'echo' => 0)), 1);  

btw, there are better ways to add classes to html tags than using regexes like this…