@turn

No, holy priests shouldn't die that often and PW:S shouldn't help that often. When raiding, the majority of the damage should always be aimed at the main tank and off tanks.

PW:S won't help worth much either. At the moment, wearing mostly 25-man naxx gear and valorous in every slot except helm(sigh), I have around 19.5k health. If something hits me and hits me for as much as 22k such as PW:S actually saves me, I'd be impresssed since most trash mobs in 25-man naxx deal between 4k to 7k dmg to me, 9-11k crit.

The boss mobs when they hit a priest such as raveious in the odd time that mc drops from both preists despite having hit cap via hit-gear for that fight and rajuveious? spelling? goes mad, he hits for around 30k and crits for around 45k. Power world shield won't make a difference whether I survive or not. Casting it more or less often in this situation unfortuantely won't save me.

Realistically, its better mana wise for the priest to take the 1-2 hits from the trash mobs till the ot/mt pulls him off you in vent as you've notified him and just do a self-cast lighter heal which if it crits does 8k healing for 500ish mana rather than 2.5k shield for 800 mana.

Personally, I'd prefer something like the Paladin's set bonus. Increased frequency of a 6 second buff giving +50% chance to critical on healing spell? I'd love to have a buff that gave me +50% chance to critical with light heals. Especially considering talented right, you could easily get 1-3 free instance casts within that period and possibly a free light/greater heal as long as it is casted within 8 seconds.