Diacritic Sensitive sort for objects fetched from core data?

If I want to sort an array of items alphabetically without the option NSDiacriticInsensitiveSearch I need to use a NSSortDescriptor with comparator

 NSSortDescriptor *sortDescriptor = [[NSSortDescriptor alloc] initWithKey:@"SortTitle" ascending:YES comparator:
                                        ^(id obj1, id obj2) {
                                            NSInteger options = NSCaseInsensitiveSearch
                                            | NSNumericSearch                    // Numbers are compared using numeric value
                                            //  | NSDiacriticInsensitiveSearch  // Ignores diacritics (â == á == a)
                                            | NSWidthInsensitiveSearch;        // Unicode special width is ignored

                                            return [(NSString*)obj1 compare:obj2 options:options];

However such NSSortDescriptor with comparator is not allowed to use in a NSFetchRequest. Therefore should I sort the results after fetching them from core data? Is this computationally expensive in terms of performance?

thanks