I thing store.add(Collection) should sort only once after all items have been added, not once for each items.
Currently when the store is repopulated with items and sorting is applied it gets really slow. Also, it seems it is possible to click on the grid header while the grid is populating, slowing the loading process form that point on considerably.
There are workarounds around this, but I think this should work without them.
ps. is there some way to prevent controls from updating while bulk loading/changing the data in store. Some thing like store.disableControls()? Store.setMonitorChanges seems to disable monitoring changes in individual model instances....