Trying to run multiple HTTP requests in parallel, but being limited by Windows (registry)

It is matter of ServicePoint. Which provides connection management for HTTP connections. The default maximum number of concurrent connections allowed by a ServicePoint object is 2. So if you need to increase it you can use ServicePointManager.DefaultConnectionLimit property. Just check the link in MSDN there you can see a sample. And set the value you need.

For quicker reference for someone. To increase the connection limit per host you can do this in your Main() or anytime before you begin making the HTTP requests.

   System.Net.ServicePointManager.DefaultConnectionLimit = 1000; //or some other number > 4

Fire and forget this method from your main method. Icognito user is correct, only 2 threads are allowed to play at the same time.

private static void openServicePoint()
{
    ServicePointManager.UseNagleAlgorithm = true;
    ServicePointManager.Expect100Continue = true;
    ServicePointManager.CheckCertificateRevocationList = true;
    ServicePointManager.DefaultConnectionLimit = 10000;
    Uri MS = new Uri("http://My awesome web site");
    ServicePoint servicePoint = ServicePointManager.FindServicePoint(MS);
}