That's why hopefully I can get the tier gear instead of the pvp gear.

Mana efficiency is based on gear not the class.

PvP for Priests = Stamina, Int, Spell Damage or Healing +
Raid for Priests = Spirit, Int, Spell Damage (Way more) or Healing +

If I can get kara/gruul/mag gear I should do well.

Before you say I'd never get into kara or a 25 man. My guild has already agreed to it. Considering I'd be an insane dps group.