Mine is currently 2 and a half hours, approximately when taking into account cutscenes and similar stuff. What's your personal best? Would be cool to hear about some insane times, cause I don't think my speedrun was particularly fast. I did a lot of things I wouldn't have had to do.

I'm currently sneaking around on the Speed Demo Archives forums. Some people already did a few speedruns, and the quickest I've seen so far is around 40 minutes for the whole game.
They are working on breaking that 40 limit in order to get a sub40 run.

I only ran the last level so far and am still trying to plan a run - there are a few "acknowledged" rules for a speedrun, so I'd like to understand them all I'm still hesitant between a full Ghost speedrun or just not giving it much thought and do as they all did : just run, not caring about being detected and just caring about going to the next marker. Which is, after all, what a speedrun is all about... ( still it doesn't feel clean in a game like Dishonored, so... yeah... Hesitant. )

40 minutes? That must be some heavily edited playthrough lol, knowing the length of the obligatory cutscenes and the fact that the Flooded District alone takes at least 10 minutes to complete.

You can skip almost all cutscenes, except I guess the boatrides at the start of each mission.
Also, it's pure speedrun, as in "any%" and no rules. No Ghost playthroughs, not Clean hand either. I feel Dishonored could use a special category just for those kind of gameplay. It's a stealth-based game, after all !

Not sure about Flooded District, I have the strangest feeling it can be wrapped up really quickly... I should try with minimum powers and charms just to be sure.
I've been reading that some people seem to have found a way to pass through some doors, I'm unsure how this factors in the speedruns though.