If you keep Power Infusion for yourself, and macro it to your shield button, you should be able to save a lot of mana. Also when you are at 50% mana left, use the shadowfiend with Hymn of Hope. Hymn of Hope increases the shadowfiend mana return by 20%.
If you do that, then you no longer need to get for INT.

I consider INT as a comfort stats, one that you use if you are not (or don't care about) properly rotating your regen abilities. Gemming for pure spellpower could increase your output by up to 25%!
As usual, double Solaces terribly help such a configuration.
If you really insist on INT then I'd recommend you gem spellpower and use the Greatness INT card. That card can return a lot of mana from rapture (+390 INT when its up) and even more if you use shadowfiend on Greatness procs.

I have Power Infusion in a macro, but not for Power Word: Shield. I combine the macro with Talisman of Resurgence. Sure, it doesn't have the pure INT that the card does, but the Use ability is nice when I hit it with Power Infusion and push out a Divine Hymn (handy in particular during Heroic Bloodqueen). And if I can get Ashen Band of Endless Wisdom to proc? Spellpower ahoy!

I'll also hit that macro JUST before I start rounds of chain healing, like 15-20 seconds before the start of the Heroic Saurfang or Lich King fights. Helps save mana, use stronger shields, etc.

I know I'm going to have to give up the Talisman sooner or later - the healing scale from Halion will probably take its place - but in the meantime, I am loving the manapool. :)

I guess it depends on what you're doing, but I'm hardly EVER even close to oom on my disc priest because of Rapture. If you're raid bubbling - even just to keep Borrowed Time up (which you should be) a big boss AoE can burst multiple bubbles at the same time, returning half your mana pool all at once.

Now, naturally I'm just starting to raid (ToC10 for gear lol) on my disc priest, but I never found myself running low (ever) because of Rapture. And though I've never raided it on my disc priest, there's so much continual AoE going out in ICC that there should be no reason Rapture wouldn't be returning mana quite frequently (I think there's an internal CD, but even with that every time it wasn't on CD or two or more shields popped at the same time, you'd get a big return).

So, I don't really see the point of that huge mana pool. You only need as much mana/regen as is required for the fight, and no more, in my opinion. On my druid (my main), I stacked haste and spirit for a long time, trying to get the (very high) haste cap while also having enough mana to last the whole fight. With better gear, I've found a good balance, so now I've started replacing some of those haste/spirit gems with haste/spellpower or just spellpower. I can't see you burning through a 41K mana pool with Shadowfiend and Hymn in ANY fight, even if you were casting straight from start to finish, so you would probably be better off getting rid of some of your wasted mana pool for more throughput. Look at your mana pool at the end of a casting-intensive fight. Do you still have 10%/20%/30% of your mana left? That's what you can get rid of. It's like overhealing - overhealing is wasted mana, but mana left over at the end of a fight is, imo wasted mana too. If your regen is too high or your mana pool is too big to get rid of, the stats that are increasing that could have been used elsewhere to make that shield absorb a little more, or that penance heal a little more or whatever.

But that's just my two cents, if it's working for you, it's your character =).

"but the shields are still so strong that I can't benefit from the regen aspect of Rapture during Lich King Infests because my shields don't fail."

ok, i might get called out for this, but i deliberately downrank my shields for certain fights. i use grid and clique and have two different strengths of shield to put up at any given time - when i need the shields to absorb an appropriate amount of damage yet be consumed totally, i use the rank 12 shield whilst still putting the rank 14 on the tanks (just in case).

seems to work, but gawd i get spammed by that rankwatch addon every damn time -.-

Int is nice, especially at lower gear levels - but it has a "cap" of its own: once you have enough mana to get through the fights you're playing, you are officially "capped". Continuing to stack int after that point is like stacking hit after a cap - it's wasted resources because it won't be used. With shadowfiend, HoH, mana pots and intelligent rapture timing, I've found I am never oom on any heroic mode fight, even though I push out every single global cooldown's worth of shields. And this is without Solace (using glowing twilight scale + hc abacus).

@spryte thats what I do as well. Thats what is recommended for LK. If you properly down rank, while doing your job of keeping infest off the raid, it doesn't matter if you used rank 1. As long as you can keep doing your job, that's all that matters, and you need your bubbles to break or you will go oom so damn fast.

I keep a huge mana pool for the same reason I keep duct tape around the house - for when stuff goes very very wrong.

And it do, it do. :)

@spryte: Wow! I hadn't thought about the down ranking bubbles. Especially for a fight like LK. Thanks for the idea :D I'm going to have to try this out later this week.

Thanks!