When I first saw Rend and Tear, I wasn't too impressed, at least from a tanking standpoint. You see, for some reason, in the back of my head, I've always thought of Mangle as producing more threat. Well, with all this talk of Rend and Tear being such an awesome talent for bear threat, I decided to look into it. Here's a fairly representative report of Druid threat, taken from a Brutallus fight:
Clearly, Maul produces the most threat, about 38% of the threat for the Druid's entire rotation. What does Rend and Tear do for this? Well, the damage goes, up and the innate threat stays the same. Since Lacerate is up pretty much all the time, it's like a flat 20% increase to Maul damage. In the case of the druid above, this increases Maul threat by about 16%. This is about a 6.2% increase in threat overall.
This seems like a decent use of talent points. You get about 1.2% threat per point. But, we're not through yet. You see, any self respecting tank will also take Imp. Mangle, which increases Mangle to occur 33% more often. This will increase the amount of damage done by mangle another 33% on average. Maul still goes up 16% with the addition of Rend and Tear. It's just that the impact of this is less, with Mangle doing more damage. In fact, in this case, Rend and Tear is only a 5.8% increase in threat.
We're still not through. Apparently, all the threat modifiers have changed. Let's rework this table to see what the change looks like all around.
With all these changes, looks like Rend and Tear is about a 5.7% increase in total threat. I can't prove this with numbers right now, but Mangle - Bear seems to be doing a lot more damage on the PTR than it used to. However, this is likely due to the Savage Fury change (though the damage seems higher than 20% more.) We'll leave the analysis here though.
I'm still undecided about moving those points. If a 5.7% threat increase is what you need to keep above the DPS as a bear, there's something wrong with your threat. Still, it does allow for more DPS to the boss. I suppose I will have to wait and see how my guild's DPS shapes up in the expansion.