Unfortunately, it's not that easy. Remember that you're putting a Devastate into my rotation instead of that Rend or Thunderclap, which means you have to compare it to the lost contribution of Devastate, taking its higher critical strike chance into account, as well as the contribution of Sword and Board procs and the potential Heroic Strikes that come from the extra rage. I'm not saying you're wrong, I'm just saying that "use Rend because of [enter number] damage" is grossly over-simplifying it.
You should try and use Thunder Clap to keep up Rend (through BnT), which actually comes before SnB fishing abilities.Especially with a Bleed debuff, you should see way more DPS out of it.
Unwavering Sentinel: Tales of a Protection Warrior Running Wild.