Packet size can be set in the TNSNAMES.ORA file and in addition at the ODBC driver level but I don't know specifically about connect packets.

Another thing to pay attention to is the order of precedence of the network protocols in the netork control panel (on server + client). Make sure that TCP/IP is top in the list.

When you use ODBC there is several additional DLL that must be loaded into memory in addition to the Oracle runtime so it will be slower than a normal SQL Plus connect no matter what you do!

If you do not have to accomodate multiple connecting clients, then you can just make a normal connection, the default type being dedicated; this is the fastest method. To prevent tns alias lookup, enter the communicating IP addresses in the tnsnames.ora and listener.ora files. This will help speed up your connection. As apposed to using host look up.

You can configure the folloing things to effect connection speed:
-ODBC or ADO
-Network
-SQL Net or Net 8
-Oracle Server

My 9i server is much faster connecting than the 8i server. I think they have changed some of the default parameters in the .ora files.

Note that connection pooling will Slow your connection done..

Just some general things that came to mind...