You can improve the performance of WebDAV by setting the following two properties of your Requestobject to false (true is the default value for both of there properties):
HttpWebRequest.ServicePoint.Expect100Continue: When this property is set to true, the Request Header is sent to the server, if it doesn't reject the request the client sends the data. If you set the value to false, the client sends the request to the server with the data. If the server rejects the request, the client must resend the complete request.
HttpWebRequest.ServicePoint.UseNagleAlgorithm: This algorithm is used to reduce network traffic. It simply buffers small packets, and sends them as a single packet, which should reduce the packet overhead.
Note: The ServicePoint class is supported only in version 1.1 of the .NET Framework.