hi Apurva, since the cascading parameters will require data for the fourth level, creating a single command object with all four required fields should be the best option.
what you may wish to do is to create a new report and just put those four fields on the report. then go to the Database menu and choose Select Distinct Records. now what is the performance like?...this should in theory be a lot better performance.
now go back to the Database menu > Show SQL Query and copy that syntax. you now have the syntax to make your Command object. to use the syntax, create a new report but this time choose Add Command (don't select any tables) and then paste in the syntax.
-jamie