Restore table sort order after app restart

Hi, i'm trying to restore the QTableView colums sort order after closing the application.
I've found a way to do that. My QTableView subclass uses lazy population (6000+ rows), i fill the model whit groups of rows until there is not more data to fetch.
When the model is full, i emit a signal, and use and slot to do proxy.sort(...) or myTableView.sortByColumn(...) ( both are slow for me ). Is de moment ok? should i sort it in another moment?
I'm little confused about why large tables in Qt are always sooo slow for me.