Breaking up the results of a loop

Question

In my query, I'm gathering 6 posts and displaying them into an unordered list. Here's the code I'm using:

$args = array(
    'post_parent' => $page_id->ID,
    'showposts' => 6,
    'post_type' => 'page',
    'orderby' => 'menu_order',
    'order' => 'ASC'
);
$subpages = new WP_query($args);

if ($subpages->have_posts()) :
    while ($subpages->have_posts()) : $subpages->the_post();
        $output .= '<li><a href="'.get_permalink().'" class="'.$page_id->post_name.'-link"><div class="'.$page_id->post_name.'-info"><div class="'.$page_id->post_name.'-img">'.get_the_post_thumbnail($page->ID,'icons').'</div><h2>'.get_the_title().'</h2>
                    <p class="'.$page_id->post_name.'-excerpt">'.get_the_excerpt().'</p>
                    </div></a></li>';
    endwhile;
endif;

I'd like to breakup the and show three posts, then insert a different div, then continue the loop. The html outcome would look similar to:

<ul>
    <li>Post1</li>
    <li>Post2</li>
    <li>Post3</li>
</ul>
<div class="notice">Some text goes here</div>
<ul>
    <li>Post4</li>
    <li>Post5</li>
    <li>Post6</li>
</ul>

EDIT I got this working with the suggestions from @Rarst. Here's my updated code:

    $args = array(
        'post_parent' => $page_id->ID,
        'showposts' => 6,
        'post_type' => 'page',
        'orderby' => 'menu_order',
        'order' => 'ASC'
    );
    $subpages = new WP_query($args);

    if ($subpages->have_posts()) :
        while ($subpages->have_posts()) : $subpages->the_post();
            $output .= '<li><a href="'.get_permalink().'" class="'.$page_id->post_name.'-link"><div class="'.$page_id->post_name.'-info"><div class="'.$page_id->post_name.'-img">'.get_the_post_thumbnail($page->ID,'icons').'</div><h2>'.get_the_title().'</h2>
                        <p class="'.$page_id->post_name.'-excerpt">'.get_the_excerpt().'</p>
                        </div></a></li>';
            if (2 == $subpages->current_post):
                    $output .= '</ul>';
                    $output .= 'test';
                    $output .= '<ul class="'.$page_id->post_name.'">';
            endif;
        endwhile;
    endif;

Answer 1

Instance of WP_Query tracks number of current post in current_post property, zero based.

So inside your loop you can check for something like if ( 2 == $subpages->current_post ) and output your additional content.