Just finished gold CM's on my pally a few days ago. Group was Holy Pally, Blood DK, Unholy DK, BM hunter and Destro Warlock. Didn't really notice mana being a problem for me, but I suspect that was helped considerably by running with 2x Army of the Dead. IMO, holy is one of the best healers for CM's just because we have the most raw power for tank healing, which is where most CM damage goes.
In any case, some tricks you can use to reduce mana spending.
- Abuse the you know what out of holy avenger. It's a massively powerful spell in CM's letting you load up the group with HoT's and funnel a lot of healing to the tank.
- FoL glyph, when you need to burst the tank quickly, that extra 10% healing means a lot.
- Just use direct healing on beacon and HS to generate HP charges. CS is nice but it's costly and doesn't do any healing.
- Clemency + Hand of Sacrifice is your best friend on large pulls for reducing tank damage
- Use and abuse Hammer/Fist of Justice. Stunned adds do no damage and damage not done is damage you don't have to heal.
I just went with my normal raidgear (after replacing trinkets and items that don't work like a helmet with a useful meta gem, etc), which was all about mastery at the time.
Haste doesn't improve your mana efficiency, unlike mastery, and it doesn't do anything more useful than mastery does, unless the people in your group are just taking completely unpredictable life-threatening damage, which I didn't have a problem with.