HttpWebRequest кодировка

request.ContentType=@"text/xml;charset=""utf-8""";

request.ContentType=@"text/xml;charset=""windows-1251""";

HttpWebRequest GRep = (HttpWebRequest)WebRequest.Create("https://www.cyberforum.ru/");
//____________________________________________________________________________________
GRep.Accept = "*/*";
GRep.Referer = "";
GRep.Headers.Add("Accept-Language", "ru");
GRep.Headers.Add("Accept-Encoding", "gzip, deflate");
GRep.UserAgent = "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1; EmbeddedWB 14.52 from: [url]http://www.bsalsa.com/[/url] EmbeddedWB 14,52; .NET CLR 2.0.50727; .NET CLR 3.0.04506.648; .NET CLR 3.5.21022; .NET CLR 1.1.4322; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)";
//_____________________________________________________________________________________
//кодировки в след. строке
StreamReader SRead = new StreamReader(GRep.GetResponse().GetResponseStream(), Encoding.UTF8); //Encoding.UTF8, Encoding.Unicode, Encoding.ASCII .... 
string otvet = SRead.ReadToEnd();
SRead.Close();

HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://vkontakte.ru");
            request.ContentType = @"text/xml;charset=""utf-8""";
            request.Method = "POST";
            request.KeepAlive = true;
 
            byte[] message = new byte[256];
            // fill message
 
            // post message
            using (Stream requestStream = request.GetRequestStream())
            {
                requestStream.Write(message, 0, message.Length);
                requestStream.Close();
            }
 
              HttpWebResponse response = (HttpWebResponse)request.GetResponse();
             using(StreamReader sr = new StreamReader(response.GetResponseStream()))
             {
              var responseString = sr.ReadToEnd();
              richTextBox1.Text = responseString; 
             }

request.ContentType = @"text/html; charset=windows-1251";

using (StreamReader sr = new StreamReader(response.GetResponseStream(), Encoding.Default))