ODBC performance InstantClient 11g vs. Oracle 9i full client

We have an application with an MS Access frontend that accesses, via ODBC, a 10.2.0.4 backend database.  Most of our workstations currently have a Oracle 9i full-client install.  We are getting pressure to upgrade to a new client, either 10g or 11g because some other applications need features that aren't available with the 9i client.  We've been testing the 10g and 11g instant client, and they seem to work well for most of our apps.  This Access application is the exception -- there we're seeing huge delays and slow performance.  Here's a message from the developer of this app:

Running an identical action in the TT app with the 9 and 11 versions, I get different response times, but identical SQL, plans and costs.