Our investigation has also revealed that creating an index on the DesignID field can significantly increase performance of Open and Save Design. These tools can be twice as fast in some cases. You will want to build an index on the DesignID field for all of your feature classes and object classes. You can build these indices using ArcCatalog or directly in the underlying database. If you build the index with Oracle or SQL Server, please remember to index both the base tables and the A tables.
If you're not a member already, I would highly suggest joining the Designer PAG to stay current on the latest and greatest performance news.