First_rows and optimization

I have found, using explain plan, that using FIRST_ROWS as the optimizer goal gives the fasted execution path in our environment. Often by a considerable amount. Oracle is v7.1.

(1) I know I can change it for a session, but can I change it for all users as they logon? The are using a variety of tools, including ODBC, so I don't think I can use use alter session as they logon.

(2) If I have the goal set to FIRST_ROWS when I analyse the table to create the statistics, does the optimiser always use the OPTIMIZER_GOAL of FIRST_ROWS for those tables, no matter what it is set to for the sessions?

This raises issues of how good is the cost based optimiser? The execution path it was choosing was clearly not the quickest path. Is the optimiser any better in 7.2? Or is FIRST_ROWS always better than ALL_ROWS?

Any advice and comments appreciated.

TIA.

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