I've not run the numbers in a *long* time, but, when the level cap was bumped the general wisdom was that Deep Wounds was worth more threat, point for point, than Cruelty (on top of Impale, of course).
From a quick re-check of talents, if you get Shockwave and Armored to the Teeth (also superior to Cruelty), you can get Deep Wounds with 2/5 Cruelty, or 4/5 Cruelty without.
Here's the thinking as I understand it. The prot tree has several talents that boost the crit chance of all your major threat tools except for Revenge. Because of this passive bump, plus raid buffs, the value of Deep Wounds can stack up and make for quality threat, where as relatively Cruelty only offers 1% crit per point to all your moves.