Split custom post list into two columns

You could count the number of items and insert </ul><ul> after 50%.

Sample code, not tested:

if ($postslist) {

    $count = 1;

    if($top) echo '<h4>'.$name.'</h4>';
    echo '<ul>';
    foreach ( $postslist as $post ) {
        echo '<li><a href="'.get_permalink($post->ID).'">'.get_the_title($post->ID)."</a></li>";
        if ( 0 === $count % 10 )
            echo '</ul><ul>';

        $count += 1;
    }
    echo '</ul>';
}

And you don’t need setup_postdata($post); here.