Hi Dom,
From the book SCEA for J2EE Technology Study Guide, it mentions that
"Because JRMP is the native protocol for RMI and does not have to support a myriad of different host data formats and byte ordering, there is less overhead in setting up the argument and return values for a call over JRMP than with language neutral systems, such as IIOP. Used correctly, this can result in higher performance."
"IIOP moves state for arguments and return values of method calls.
� JRMP moves state and behavior (whole objects) for arguments, return values, and exceptions in method calls.
� JRMP is a native Java technology protocol, so it has less overhead than protocols that have to perform format conversion."
Hope this could help
KH