I always though the 10 int 10 spirit were the best gems and the 12sp and 10 int were the only way to go with geming priests. But, I'v noticed a lot of holy priests going with the 12 SP and 10 spirit instead of the 10 int 10 SP and even geming for straight Spell power. Any advice or suggestions would be great!
There's a lot of flexibility in the way Holy priests gear. Generally though, Intellect is your main mana stat simply because most of your mana regen abilities (Hymn of Hope, Shadowfiend, Replenishment) are based off of your total mana pool. Spirit is nice for a mix of mana and spellpower, but nothing that you want to give precedence to.
Spellpower is usually your #1 throughput stat. If you don't have mana problems, gem for throughput.
Are you having mana problems? If you are finishing long tough fights with a significant amount of mana left, it's time to regem for more throughput. You have pretty nice gear, I think you could start by tossing out a handful of orange gems for red gems and see how that impacts your mana pool and your healing done.