I'm specc'ed holy/disc combo for better shield and bonus dmg and lower mana cost on holy nova; on trash in UB I was doing 1.5k dps with each level 64 priest just spamming holy nova; which is higher than some of my level 80 guys (but obviously a gimmick of the aoe) - this is what keeps my guys alive when hit by tons of melee, pain suppression also helps (for AV too) - boss fights are a bit harder as you can see from the screen shots :-)

My girls are 69 now so I can try some of those dungeons soon (though I don't have the key for shattered halls... I guess I can do the quest line maybe or find a rogue or someone to open)