Some items have movement speed and some characters have movement speed buffs or skills. What is the fastest movement speed you can have in Diablo 3?
There's a hard movement speed cap of 25% from items. Skills and passives can surpass that limit though. Movement speed bonuses from items stack additively, but I don't know how skills affect it afterwards. I believe the highest possible would be a combination of these (I may be wrong):
If they do in fact stack additively for skills as well, then you could get a total of +105% movement speed.
Big Bad Voodoo is an immovable totem pole with a large aoe, it won't be very helpful after you leave its range.
Barbarian's Sprint (costs 20 Fury) ability with the Marathon rune allows for 50% movement speed for 5 seconds. Without the rune, it's only 40% for 3 seconds. With some serious Fury regeneration gear, that could wind up being a pretty reliable and mostly active ability for those high levels trying to do the speed run achievements.
Though I am also unsure if movement speed gear stacks with the ability (total of 75%), or if the ability just enables the movement speed cap to rise while the ability is active...