As a general rule, speed buffs never stack. The description on the cloak even states, "Increases the run speed of the wearer. Does not stack with other run speed augmentations." There are a few cases in which speed buffs will stack, but those are generally temporary buffs. Static bonuses on items (such as the Bogstrutter Walking Stick) will stack with the buffs.
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(Fyreflyte) Re:Kurn's cloak of speed
