Is SOAP the best RPC to use between a Java app and a COM based app?

[TheRookie]

I have developed a Java application that needs to communicate with a
pre-developed C++ based application. Currently, the C++ app only
supports SOAP as a communication means. I am looking for benchmarks
showing that alternative RPCs (Java to DCOM?)provide superior
performance. Anyone have any data supporting this, or any ideas where
I might find them? Even some tools to test this would be great.

Thanks.