超级郁闷之问题，请DUDU及各位大位指正错误

事情皆因一文件下载惹的祸。首先我介绍我的机器构成：文件服务器，暂叫A服务器，也就是放文件的机器。应用程序服务器，这大家都明白，就是部署程序的服务器，其它服务器就不说啦。
好，开始说问题，最初小弟，根本没去想太多的性能与服务器的承载量的问题。就写了下面两段代码

string physicalFilePath = downloadpath;
                FileStream stream=null;
                try 
                {
                    stream = new FileStream(physicalFilePath, FileMode.Open, FileAccess.Read, FileShare.Read);    
                    int bufSize = (int)stream.Length;
                    byte[] buf = new byte[bufSize];

                    int bytesRead = stream.Read(buf, 0, bufSize);
                    HttpContext.Current.Response.ContentType = "application/octet-stream"; 
                    HttpContext.Current.Response.AppendHeader("Content-Disposition", "attachment;filename="+Server.UrlEncode(System.IO.Path.GetFileName(Server.UrlEncode(filename))));
                    HttpContext.Current.Response.OutputStream.Write(buf, 0, bytesRead);

                    

                    HttpContext.Current.Response.End();
                }
                finally 
                {
                    stream.Close();
                }


或：
downloadpath为变量
System.IO.FileInfo file = new System.IO.FileInfo(downloadpath);
                    Response.Clear();
                    Response.Charset="GB2312";
                    Response.ContentEncoding=System.Text.Encoding.UTF8;
            
                    Response.AddHeader("Content-Disposition", "attachment; filename="+Server.UrlEncode(filename));
                    Response.AddHeader("Content-Length", file.Length.ToString());

                                    
                    Response.ContentType = "application/ms-excel";
                    Response.WriteFile(file.FullName);
Response.End();

刚开始放上去时，根本没有任何问题，因为访问量与数据文件都不够大。
等过几天，访问量达到几千人同时在线时，我的问题来啦，有的数据文件也比较大，有的是100M以上的，哪上面这两种方法同时挂掉，有的因为文件太大，而无法输出，有的的有时莫明其妙的弹出服务器重置这种提示，后来我又换啦一种下载方式，代码如下：

#region
        public static bool ResponseFile(HttpRequest _Request,HttpResponse _Response,string _fileName,string _fullPath, long _speed)
        {
            try
            {
                FileStream myFile = new FileStream(_fullPath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite);
                BinaryReader br = new BinaryReader(myFile);
                try
                {
                    _Response.AddHeader("Accept-Ranges", "bytes");
                    _Response.Buffer = false;
                    long fileLength = myFile.Length;
                    long startBytes = 0;
     
                    int pack = 10240; //10K bytes
//                    int sleep = 200;   //每秒5次   即5*10K bytes每秒   1024000
                    int sleep = (int)Math.Floor(1000 * pack / _speed) + 1;
                    if (_Request.Headers["Range"] != null)
                    {
                        _Response.StatusCode = 206;
                        string[] range = _Request.Headers["Range"].Split(new char[] {'=', '-'});
                        startBytes = Convert.ToInt64(range[1]);
                    }
                    _Response.AddHeader("Content-Length", (fileLength - startBytes).ToString());
                    if (startBytes != 0)
                    {
                        _Response.AddHeader("Content-Range", string.Format(" bytes {0}-{1}/{2}", startBytes, fileLength-1, fileLength));
                    }
                    _Response.AddHeader("Connection", "Keep-Alive");
                    _Response.ContentType = "application/octet-stream";
                    _Response.AddHeader("Content-Disposition","attachment;filename=" + HttpUtility.UrlEncode(_fileName,System.Text.Encoding.UTF8) );
 
                    br.BaseStream.Seek(startBytes, SeekOrigin.Begin);
                    int maxCount = (int) Math.Floor((fileLength - startBytes) / pack) + 1;

                    for (int i = 0; i < maxCount; i++)
                    {
                        if (_Response.IsClientConnected)
                        {
                            _Response.BinaryWrite(br.ReadBytes(pack));
                            Thread.Sleep(sleep);
                        }
                        else
                        {
                            i=maxCount; 
                        }
                    }
                }
                catch
                {
                    return false;
                }
                finally
                {
                    br.Close();
                    myFile.Close();
                }
            }
            catch
            {
                return false;
            }
            return true;
        }
        #endregion

这是从网上看到一位同仁写的，就拿过来一试，发现对大文件下载，还真不错，能顺利下载，好一段时间都没问题，心想这下可好啦，但没成想，好日子没几天，问题又接二连三的回来啦，这次的问题更莫明其妙，有的是下载到99%时，突然提示不能下载，有的呢，却一点击下载，弹出框后，就一点进度都还没有时，就一会儿弹出来一个连接超时，服务器重置的提示，把我给郁闷的，但同时呢，其它文件又可以下载用同一段代码。郁闷中ing....希望有哪位能指点一下。
文件肯定存在，链接肯定正确