Handy Hint:

Please, try not to use the System.XML.XmlDocument object inside an orchestration, or receive messages of this type. This object is not very well  performing, and requires you to load the entire message into memory.

Try and use an envelope schema, or a basic schema with an any tag inside it, something that can identify the message, rather than an xml document object.

I see the use of this all over, and it can bring a system to a halt when it come to super fast performance requirements.