I dual healed the first four bosses the other night (Holy Priest[me] + Mistweaver Monk). The Monk was doing around ~30% more healing than me, had ridiciulous amounts of overheal that he didn't care about (I'm talking 10-15 time more than me) while still never complaining about mana. This is the person whom I regularly beat in Dragon Soul when he played a Disc (we raided with two healing priests in 10 man, lol). Take from that what you will.
World of Logs says Mistweavers and Holy Pally are doing pretty well. I'm also a little skeptical of the 47k to 56k on the fourth fight...considering no one logging on WoL 10 man has more than 47.5k heals on Spirit Kings and the highest ranked holy priest has less than 40k.