http://youtu.be/b-e32KD35-Q
Last level done in 2:30 from the moment we are given control to the moment we open the door to Emily's chambers.
I had to pick some powers first, since I first did the game in very hard / mostly flesh and steel. I do not count this little manipulation in the countdown.
One thing that actually bothered me a little in Dishonored was that, even with multiple paths, one was always way, way quicker and almost safer than the rest.
During the High Overseer mission, when you reach Hoger street where there actually is the high Overseer, you can just hop onto the ledge and get a complete access to both the interrogation room ( which conveniently contains a book about the Heretic Brand, no need to go to the Archives ) AND the dinning room where Campbell meets with the Captain.
During the Sokolov abduction mission : there is a chain that will bring you straight from the roofs of the nearby buildings to the greenhouse where he is experimenting. So, yeah, you miss the whole house, but there isn't even much to see there. The painting can even be stolen on the way down thanks to an open window.
During the Lord Regent mission, once inside the palace, you just blink on the lamps, then in the LR's room. The broadcast tower is also easily reachable.
For the final level, well just look at my video. I'm quite confident this can also be done with nothing more than just Blink 1. Actually I almost did. But for the sake of "speedrunning", Blink 2 and agility 2 are obvious requirements.
While I strongly support the "take the route you want" approach in a video game, I also am a bit disappointed that sometimes, there IS a direct route which is obviously the "best", since you don't miss so much stuff, and you still can manage to do the mission safely.
Maybe they could have avoid such direct routes. Maybe I'm just a bit disappointed by this fact. Don't get it wrong, though : I LOVED Dishonored. This here is merely the only thing that annoyed me in the end.