jQuery Grid Plugin - jqGrid

I have a "report writer" type of page where the user sets various options which are used to retrieve data to load into the grid.  Depending on what the user selects, the column model may or may not change for subsequent reports.  (For example, if the user just changes the dates, the column model will not change.)  If the columns do change, I know that I need to unload and then respecify the grid, right?  If the columns don't change, I can use setGridParam to change the url for the ajax call and then reloadGrid.  Is this more efficient/faster than unloading?  Is it worth putting logic in to check whether the column model has changed (in order to avoid an unload)?