Efficient way to update multiple post meta

I have managed to update post meta using update_post_meta(). However, the more posts I have, the more time it takes. I would like to minimize the time it takes to process say about 400 posts (although I am not too sure how long this will take). Currently my code looks like this:

    $numbers = range(1,100000);
    shuffle($numbers); //Randomizing the index (no duplication at all)

    $count = 0; //Begin with an index of 0

    $args = array(
        'post_type' => 'xn_group',
        'post_status' => 'publish'
    );


    //This should get all the posts of xn_group, all of these posts will get the value of its meta_key 'xn_group_order' shuffled (randomized daily).
    $the_query = new WP_Query($args);

    //DIRECT QUERYING...(to reduce time complexity)

    while($the_query->have_posts()) : $the_query->the_post();

        update_post_meta(get_the_ID(), "xn_group_order", $numbers[$count]);
        //$count += mt_rand(1,10); //Another technique to ensure fair randomization (not necessary).
        $count += 1;

    endwhile;

    wp_reset_query();

However, I worry that as posts get bigger, the changes made will cost a lot. So I would like to ask the better way to achieve this. Perhaps using SQL statement? Any ideas?

Perhaps using SQL statement?

Direct SQL queries are very dangerous, especially when updating the DB. At the very least you will get any object cache out of sync and you might miss execution of import action and filters.

If this update is something that is rarely done it is better that it will take one more minute then to risk the integrity of your system.