My healing build is Int > Mastery > Spirit > Haste - 6694 Int, 15.10 Mastery and 2695 Spirit. All unbuffed. My haste is pretty low (1281 or 10%). Glideroy said that this CC is designed for Spirit / Crit Holy Paladins, and said that Haste burns mana faster because the CC doesn't delay in healing - thus you keep casting and casting, losing mana faster. Also, don't get more than 15% crit. 15% (20%+ with raid buffs) crit is good enough for proccing Conviction almost all the time.
I've been topping healing charts ever since with my Mastery build. Slower casts but more effective heals. Since the CC reacts pretty quick, the slower casts (due to low haste) doesn't matter.
I barely OOM too. The settings I changed: Holy Light to 90%, Divine Light to 85%, Flash of Light to 40%, Infusion of Light (Divine Light) to 75%, and tank priority to 70% and 0% Multiplier. This is just the general stuff. Why higher %? Because Mastery works nicely and better with Divine Light, Flash of Light and Holy Radiance. So, use these spells more often than Holy Light - since Holy Light is an inexpensive/very little heal and the fact that you'll slow cast, it's better not to use Holy Light a lot.
Also, while you're slowly casting (again due to low haste), you're still regening mana and still giving the CC more time to decide what spell to use next. Understand what I mean?
tldr: Too much haste (1300+) you'll burn mana faster because the CC is designed for Spirit. Prioritise on Mastery and Spirit instead. Don't use more than 15% crit.