Informix 7 to 9 upgrade question

I have a client who has jsut done a 7-9 upgrade. I am told they did not make any code cahnges, and performance numbers look comparable to 7 performance, if not slightly better in some cases. The problem is that the users are seeing slower response. The application provider has stated that his other clients have not seen any performance change with this same upgrade. Their exisintg clients from what I can gather are running with shared memory connection, where as the existing client has an app server where the application runs from. I personally did not do the engine upgrade, their app vendor did that. What I have seen is that there are numerous network alerts on the box since the upgrade. I have verified the normal things like stats, cache hits, and NET connections are running on CPUVP's not NETVP's. We are not able to nail this down to a specific query or application for that matter, what we see seems to be load related. My real question is first, what network overhead increase if any is ther between 7 and 9 we have not received a definative answer from informix at this point. Secondly, what other tuning have you seen required for a 7-9 upgrade. these are rather small databases in general, but response is expected to be fast. There is less than 60% memort utilization, and disk utilization is rather low in general. They are connected to a SAN with and EMC Symetric on the back end. Thanks, Tony