I've also finished the game, and i did all activities. My percentage is now 96%, and i suppose the last 4% are supposed to come from that last "mission".
Could anybody here verify that after doing all activities the maximum percentage to get is 96% ?
PS. i advise everybody to play all activities first before you start doing the missions. That way you have a asskicking character with lots of free guns and infinite running etc before you even start doing the missions.
So you'll have much more fun during the missions, and you won't have to let any enemies live due to low health, because your character will be strong as a beast