I managed to luck out and get 100% completion after a couple of attempts, but its truly a pain in the a** to get. However, I felt the perfect ending was worth it.
If you end up giving it another try, my advice is to follow a guide very closely and save your game in several spots. If the guide says after said mission that you'll be 19.2% complete and the game tells you "mission complete 19.2%", save your game and do not save over that file. Trust me, you will get to a certain point in the game where the guide will tell you a certain % and the game will say a different % after said mission. In short, with the loads of missions in this game, it's inevitable not to mess one up.
Perfect Ending:
http://www.gametrailers.com/umwatcher.php?id=31289