Can SimpleXML load only a partial of a XML?
$feed = 'rss file';
$xml = simplexml_load_file($feed); //not the entire feed though

$xml   = simplexml_load_file($feed);
$top10 = $xml->xpath('/rss/channel/item[position() <= 10]');

foreach($top10 as $item) {
   // output $item;
}

$xmlr = new XMLReader();
$xmlr->open('path/to/file');
// ...
// move the pointer with $xmlr->read(), $xmlr->next(), etc. to the required
// elements and read them with simplexml_load_string($xmlr->readOuterXML()), etc.
// ...
$xmlr->close();