What is the fastest way to get the number of items in an iterator?

I have a folder structure with something over 300.000 files and folders in it.

When I iterate over this structure to get all files of a certain type, this take about half a second to complete:

$path = "/path/to/folder";

$folder = new RecursiveDirectoryIterator($path);
$iterator = new RecursiveIteratorIterator($folder);

$files = new RegexIterator($iterator, '/^.+\.jpg$/i', RecursiveRegexIterator::GET_MATCH);

But getting the length of the resulting iterator ($files) takes about ten seconds:

$n = iterator_count($files);

Is there a faster way to get the number of items in the iterator? Maybe during iteration?

These all take around 10 seconds, too:

1. find (commandline)

find /path/to/folder -type f | wc -l

2. scandir (PHP, source)

$intFileCount = countFilesInDirectory($path, array('jpg'));
echo $intFileCount;
function countFilesInDirectory($strPathToDirectory, $arrExtensions) {
    $intFileCount = 0;
    $arrFiles = scandir($strPathToDirectory);
    foreach($arrFiles as $strFile) {
        if('.' != $strFile && '..' != $strFile) {
            if(is_dir("$strPathToDirectory/$strFile") && is_readable("$strPathToDirectory/$strFile")) {
                $intFileCount += countFilesInDirectory("$strPathToDirectory/$strFile", $arrExtensions);
            } else {
                $arrFileInfo = pathinfo($strFile);
                if(in_array($arrFileInfo['extension'], $arrExtensions)) {
                    $intFileCount += 1;
                }
            }
        }
    }
    return $intFileCount;
}

Note:

I'm counting the seconds in my head. So there might be some slight difference between methods, but it is not so large as to be relevant to me.