Microsoft come out with a new paper of comparing performance of WS in Microsoft platform and on IBM WebSphere.
MS comes out better (the purple bars graph) but then that is not surprising since this is an MS paper

An interesting point is to see the comparison of different WCF configurations. Using NET-TCP gives almost double performance then using HTTP and self hosting http also gives a bit more then IIS hosted services.

Another significant point is that they calculated performance you get for what you pay for it and then MS solutions comes out the better deal by a few scales (the graph with the green bars).

More details in the spec here