I haven't performed load testing on the order that you mention, but I'm anxious to try. :-) The most important factor in performance is how the application is designed and implemented. A few choices in the wrong direction can drag the fastest bare bones architecture down to tortoise pace. Serialization, parsing, transformation, encoding, and synchronization are common culprits in both runtime and application code. My advice would be to create a basic app that mimics the important parts of your deployment environment (bindings, implementations, message types) and then just beat on it to get a sense of how it will perform.
Kishore, did you do some load test of SY? Could you provide some results you achieved?