I'm not going to give you numbers - instead, I'll give you an easy way to generate the numbers in your environment.
Attached is a VS 2005 Solution which you can use for testing. Have a look in the Program.cs file. The code is pretty self-explanatory. You need to give a list of paths to the IDocs you want to test with, and you need to enter the SAP Server details. The IDocs have to be in Flat-File format - the first line representing the control record, and then each subsequent line representing a data record.
You need to add references to Microsoft.Adapters.SAP.dll, Microsoft.ServiceModel.Channels.dll and System.ServiceModel.dll (for the SAPBinding); and SAP.Connector.dll (the SAP .NET Connector).
You also need to have both RFC SDK Libraries present - Unicode + NonUnicode. The SAPBinding uses the Unicode Library, while the SAP.Connector uses the NonUnicode Library.
Once you've carried out the above two steps (i.e., corrected the paths in the code to point to your IDocs, and added references to the above mentioned DLLs), compile and run the program. The latencies for sending IDocs via the .NET Connector, and the SAPBinding, are displayed.