Resolution:
Process callbacks are about twice as fast as subject callbacks and are also more efficient. With subject callbacks, when a message arrives at its destination (which may be wild carded) it must be matched against all existing subject callbacks(which may also be wild carded). This is an expensive operation. To add further expense, each matching callback must be re-created and added to a new callback list in order to preserve ordering based upon priority and to prevent duplicates. If speed and time is of concern, process callbacks are recommended over subject callbacks.