Alter query using pre_get_posts() if meta_key is present

Based on data from your Gist, the following pre_get_posts condition should work to limit your posts per page.

add_action( 'pre_get_posts', 'my_set_category_posts_per_page' );

function my_set_category_posts_per_page() {
    global $wp_query;

    if ( 'category_sticky_post' === $wp_query->query_vars['meta_key'] ) {
      $wp_query->set( 'posts_per_page', 8 );
    }
}