I think there was a misunderstanding. I remember Jack, or was it someone else, recommending SoC for a Prot Pally
to grind with.
Because, sure, most of the time you'll be using your tanking gear and taking on multiple physical mobs, but sometimes you'll have to deal with casters and so then you may find it better to use a two-hander and switch some gear in favor of Warr/Retro-oriented stats.
That being said, indeed, no one would/should recommend it for tanking purposes.
As you'll get closer to 70, you'll find that SoC will indeed will worse than SoR since you pretty much should have no melee DPS stats. That's why you'd have a separate set. And with that separate set, I'd guess SoC would help killing stuff more, but I don't wanna do the maths really. Let's just address a few concerns:
SoC vs SoR, threat - SoR is reliable, SoC isn't. For tanking, SoR is the way to go with SoV if you're Alliance. (Which you aren't anyway so blah)
SoC vs SoR, DPS - SoC should do more burst damage, but as a Prot Pally tank with decent SpellDmg, you'll find you do good damage just by tanking. If nothing is hitting on you, though, you're gonna be on par with a kitten.
SoC vs SoR, coefficients - SoC is 20% but it's gonna change to nothing in 2.3 (as far as I know) and SoR is 9.2%.
Soooo... conclusion is, since you're Retro, go with SoC. It's in your talent tree for a reason. Once you get high enough level, use Seal of Blood for DPS but you might wanna keep SoC for PvP.
Oh and hey, I think I found the thread Jack posted in, so I'll quote it in case he doesn't see this and can't answer himself. I'll try to quote in small characters this time so it doesn't take as much place.
CapJack wrote:
2 sets of gear, one a solo-dps set, and the other an aoe-tanking set.
The Solo-dps set would stack on lots of melee attack power, crit chance, the normal stuff just think "Arms Warrior", this will allow you to grind down annoying spellcasters and individual mobs faster than your...
CapJack wrote:
I did 61~68 as a 10 holy/xprot/11 ret, which allowed me to tank in instances, and have SoC for soloing. Had two sets of gear for tanking and for dpsing. Reckoning, when it procced, would usually take out about half the mobs health by the time it was over, especially with an SoC proc almost every time, 3 hits for the price of one.
That's what I had at 61, with my next 5 points would be going into Argent Defender, then I respecced again at around 67 or 68 to take out my Ret Talents as I found that SoB was better than SoC, and the patch for Imp. Holy Shield came out, then when I hit end-game I went into a 21holy/40 prot build for a while, until I settled into the spec I have now.