multiple inserts are faster but it has thredshould. another thrik is disabling constrains checks temprorary make inserts much much faster. It dosn't matter your table has it or not. For example test disabling foreign keys and enjoy the speed:
SET FOREIGN_KEY_CHECKS=0;
offcourse you should turn it back on after inserts by:
SET FOREIGN_KEY_CHECKS=1;
this is common way to inserting huge data. the data integridity may break so you shoud care of that before disabling foreign key checks.