Async `curl` requests

I use parallelcurl.php (https://github.com/petewarden/ParallelCurl) library to send async requests to server. My code :

$urls = array('link1','link2'...'link100');
function on_request_done($content, $url, $ch, $search) {
            $code = curl_getinfo($ch,CURLINFO_RESPONSE_CODE);
            $size = curl_getinfo($ch,CURLINFO_SIZE_DOWNLOAD);
    echo "Code : ".$code." Size : ".$size."<br>";
}
$max_requests = 1;
$parallel_curl = new ParallelCurl($max_requests);

foreach ($urls as $url) {
    $parallel_curl->startRequest($url, 'on_request_done');
}

$parallel_curl->finishAllRequests();

I did some experiments with max_requests parameters and faced to situations where max_requests=1 and max_requests=1001 needed same time interval to send requests and get response. I thought, that if max_requests = 100, requests-response will more quickly, but I was wrong. May be I use this library not correct ? How can I send more requests use php?

For Example - if I use jMeter I can send more than 4000 requests in min. is this possible in php?