With the arrival of 4.1, we finally see the change to our Holy 4pc T11 bonus. I commented on this back in March, but I though it'd be worth touching on again in case someone missed it. In short, the 4pc bonus now grants 540 Spirit for 6 sec, every time you cast Holy Shock. Since we should be casting Holy Shock every time it's off CD (assuming we're healing) this will be a nice boost for us. Since realistically you're probably looking at more like a 50% cast time, it's still a nice bonus.
Show me the math
So the formula for calculating mp5 is rediculous, and I'm pretty sure that I screw up the order of operations half the time, but here it is.
.0025 + SPI * sqrt(INT) * .0083625 Of course I've also found this formula .016725 * sqrt(INT) * SPI
Either one makes my head hurt, but what I do know is this. I get about .33 mp5 (in combat) per point of spirit. So a bonus of 540 SPI will give me about 178 extra mp5. This of course is calculated by dividing the bonus mp5 I get from Spirit by the mana regen I get while in combat. So this number is probably wrong as well.
Either way this should, at a minimum, provide a minimum of 270 SPI for the duration of the fight, and that's nothing to sneeze at - especially if you aren't getting the heroic drops. You can certainly push the SPI return up if your HS is consistantly cast as soon as it comes off CD, but the math makes that tough. Even with a 2 sec cast on DL, as soon as you use an instant your ability to cast immediately after it's available will be tough. It would have been nice of Blizzard to make the duration say, 8 sec, so we could keep the buff up full time.
So is it worth getting?
This goes back to the debate about the T11 in general. With the small buff to Mastery in 4.1, I think the T11 gets a little more love, though I'm still not crazy about our Mastery. Personally I'll be swapping to my 4pc, at least until Chimaeron drops my shoulders (Heroic version) - and then it'll be time for some serious math.