Performance will be massively improved by moving logic into the stored procs, especially if explicit transactions are involved.
In my experience, application developers aren't very good at writing optimised database code, and don't tend to think about concurrency or performance issues.
If business logic is kept in the application layer, you tend to have to shift large amounts of data (often in many round-trips) across the network, duplicate it in memory on the DB server, and at least once in the app server, and do a load of row-by-row processing in the app while you're holding open a transaction. Then the app developers complain that the database is slow and keeps deadlocking.
If you put the logic in the DB wherever it's possible, you tend to just pass a few parameters across the network, transactions aren't held while you wait for network resources, and the whole thing goes like greased lightning.
Databases should of course go in source control like any other source code.. there are plenty of tools for that.
