Skipped drinking all together, too much downtime, it's also a question of how long it takes you to clear the same instance.

I can kill elites with 5 shaman group, 1 restor and 4 enhancements and maybe drink once in awhile, but once my mana goes down, the time it takes to kill the mob after elite #4 isn't as good as elite #1. After elite #6, it's just meleeing and shock everyonce in awhile.

On the other hand, 70 mage and 4 shamans could pretty much take out Cathedral in 10-12 minutes flat, multiply that 110-150xp times the entire instance of mobs vs 5-7 mobs then drinking and you're current xp. Since I clear so fast, I have to actually do Armory, then Cathedral, reset, do Cathedral then back to Armory or I would reach my instance cap very fast.

Then at work I can solo grind the 5th shaman since I can't exactly multibox at work.