I'm trying to change up the review list block on our website such that it only displays the top three latest four star or higher reviews.

Currently I am trying to go about this in the following manner:

    $_store_id = Mage::app()->getStore()->getId();
    $_reviews = Mage::getModel('review/review')->getResourceCollection();
$_reviews->addStoreFilter($_store_id)
        ->addStatusFilter( Mage_Review_Model_Review::STATUS_APPROVED )
        ->setDateOrder()
        ->addRateVotes();
// prepare for ratings
$_reviews->getSelect()->join(array('ratings'=>'rating_option_vote_aggregated'), 'main_table.review_id=ratings.primary_id', array('percent_approved'));
$_reviews->getSelect()->where('ratings.percent_approved >= 80');
echo $_reviews->getSelect();
$_reviews->load();
    <?php if (count($_reviews)):?>
        <h2><?php echo $this->__('Our Top Favorite Reviews') ?></h2>
        <ul>
        <?php $i=0; foreach ($_reviews as $_review):?>
        <li>Each review goes here</li>
        <?php endforeach; ?>
    <?php endif; ?>

The gist of it is that I want to perform a join with the aggregated ratings table and have a filter to strip out the reviews with a rating under 80%. The problem I'm having is that even though the echo $_reviews->getSelect(); outputs the desired SQL, the $_reviews object count does not change or even filter out these reviews that are under 80%.

Here is the outputted SQL:

SELECT `main_table`.*, `detail`.`detail_id`, `detail`.`title`, `detail`.`detail`, `detail`.`nickname`, `detail`.`customer_id`, `ratings`.`percent_approved` 
FROM `review` AS `main_table` 
INNER JOIN `review_detail` AS `detail` 
    ON main_table.review_id = detail.review_id 
INNER JOIN `review_store` AS `store` 
    ON main_table.review_id=store.review_id 
INNER JOIN `rating_option_vote_aggregated` AS `ratings` 
    ON main_table.review_id=ratings.primary_id 
WHERE (store.store_id IN('1')) 
    AND (main_table.status_id=1) 
    AND (ratings.percent_approved > 60) 
ORDER BY main_table.created_at DESC

Does anybody have a clue why my select statements on Mage_Review_Model_Resource_Review_Collection aren't taking place? I've already tried modifying to core file app\code\core\Mage\Review\Model\Resource\Review\Collection.php to make these changes through a function call, however that didn't work either.

Magento ver. 1.7.0.2

I'm feeling quite stumped and could use some help. Thanks in advance.