Here, I talk about Rend in a farming efficiency method. As some of you already know, Alkaizer was the first to popularise Rend as an AoE mechanic for XP farming. By using the Ravage rune, Alkaizer was able to expand the AoE damage to 17 yards instead of the normal 10 (could be wrong on this though) -- in effect, accumulating XP bonuses from a massacre streak. It also allowed him to dump fury and re-up by simultaneously hitting Battle Rage and Rend. That's a total of 40 fury for a gain of 1 second of Wrath uptime.
Now, I have been using Rend for awhile now (thanks to Lorenze who finally got me to commit to dumping War Cry a long time ago). It's an amazing AoE skill that absolutely puts Overpower to shame, allowing you to do massive damage on kiting creeps. A critical hit can do millions of damage and you can carry on with your business.
Tonight, a good friend of mine got a drop. It was this incredible Stone of Jordan that made my jaw drop: http://i.imgur.com/wW0zh.jpg
At first, I only saw the cold damage and figured it would help my Whirlwind management on condensing the creeps for more 'effective' damage. And that's really all it was -- until I saw my friend use the new Stone of Jordan to do this: http://www.twitch.tv/r1ckrolled/b/339994903
By condensing the packs together (i.e., slowing them down), Rend has far more effective damage with an Echoing Fury. You might be keenly aware of the fear procs that come with the Echoing Fury. I have it equipped in my main-hand -- my friend has his in the offhand. The fear procs can be difficult to manage and annoying to try and resolve. There are times I tap Rend and come up empty due to the fear procs.
No longer. Out of surprise, I picked up a 27% bonus to elites cold damage Stone of Jordan for 80m right after I watched the stream. The damage I do is vastly more effective for the reason in the last paragraph.
Compare the two: http://i.imgur.com/1Mrbj.png
I choose to keep the 27% one :)
I highly highly highly recommend that if you do use Rend and an EF, pick up a cold damage SoJ.
Oh, and for the record, my Rend + Battle Rage fury cost is 35 for a 1 second gain of uptime.