Rune of Unending Thirst

Just tested this as frost DW, the 5% run speed does NOT stack, and when you kill a target you get healed twice but only 1 haste/run speed buff. Don't use 2 of these, put this on your OH if you are DWing.

Rune of Unending Thirst only seems to proc by your own killing blows, I've never seen it without [spell=101568] proc at the same time.
Could be nice for questing, but for dungeons I'll prefer Rune of the Fallen Crusader.

The buff that procs upon killing blow is really bugged/inconsistent when it comes to stacking.
It stacks with gear that has bonus speed stats or speed enchants (e.g. cloak enchant), but it won't stack with the speed gems that give 3% or 5% buff. It WILL stack with the SL gem that increases speed per SL gem equip, but it won't stack with soulbinds that buff speed in some way.
It will stack with speed potions but not Death's Advance or Wraith Walk.

EDIT: Its more confusing than I thought. The 10% proccd buff does stack with speed pots and Deaths Advance, but the flat 5% buff you get from this enchant won't. So some of the stacking bugs are with the 10% killing blow buff, some are with the flat 5% default buff you get. Super confusing.