Hi Carlos,
If you want best performance , expose RFC as Webservice in ECC. you will have two advantage
1. Response time will be very less (As communication is between source and ECC system only).
2. Logging of messages will be decreased.
If using of PI system is mandatory in your project , Create SOAP to RFC scenario and maintain Message prioritization in RWB . Message prioritization will help to process message quickly.
Thanks
Hari.