What hook should be used to programmatically create a post only when master post is updated?

Pippin and Jean-Baptiste Jung have very good tutorials on how to programmatically create content when a new post is published using these four actions hooks…

• publish{post_type}
• add_action(‘new_to_publish_{post_type},
• add_action(‘draft_to_publish_{post_type},
• add_action(‘pending_to_publish_{post_type}

… to run this script…

global $user_ID;
$new_post = array(
    'post_title' => 'My New Post',
    'post_content' => 'Lorem ipsum dolor sit amet...',
    'post_status' => 'publish',
    'post_date' => date('Y-m-d H:i:s'),
    'post_author' => $user_ID,
    'post_type' => 'post',
    'post_category' => array(0)
);
$post_id = wp_insert_post($new_post);

What hook should I be using to do this function only when a post is updated?
Thank you!

you can use pre_post_update action hook like so:

add_action('pre_post_update','post_updating_callback');
function post_updating_callback($post_id){
    global $post;
    // verify if this is an auto save routine. 
    // If it is our form has not been submitted, so we dont want to do anything
    if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) 
      return;
    if ($post->post_status == "publish"){
        //do update stuff here.
    }
}

Update:

instead of wp_insert_post() use wp_update_post like this:

//first get the original post
$postarr = get_post($post_id,'ARRAY_A');

//then set the fields you want to update
$postarr['post_title'] = "new title";
$postarr['post_content'] = "new edited content";

$post_id = wp_update_post($postarr);

this way you only need to specify the fields that were updated and never worry about stuff like what was the original post type.