Just for a last thought for anyone reading this post as much as anything else.
At a high level or architectural standpoint the use of an integration engine in these types of scenario's cannot be understated. Regardless of which system is used be it SAP PI, WebMethods or some other technology is crucial for many reasons some of them listed below off the top of my head;
1. Security - allow direct access to your ECC/CRM system is dangerous. Access to a subsystem/integration engine with its associated security libs around services is ideal.
2. Scale up and out - Far more cost effective to have a integration engine double in size then your entire infrastructure.
3. Transactional/Transformation load - better this is pushed onto a another system - crashing SAP PI by somehow overloading it is bad, crashing ECC/CRM will effectively stop everything. Even its not a crash just a slowing over the system due to a influx of messages being able to or limiting the impact on users of the system by controlling/dealing with it in PI is a far better situation than hurting ECC with this stuff.