score:3
Middle names are generally considered optional in flight booking; if your first and last name match, there should be no problems.
Of course, nobody can guarantee that you don't hit the most anal check-in person in the world, and he won't let you board - there is no international law that forces them to. But I haven't entered my middle name ever, and flown over 500 times in 40 countries the last ten years, without anybody ever even mentioning it.