Helloo. My guild is now getting into Hardmode 25 mans. My main question is, Disc or Holy? What is more valuable, the mitigation from disc or the throughput holy gives? I am raid healing all the time whether I am disc or holy, so what is more effective?
As always, the proper answer is "whichever you find more fun".
If you have no preference at all, well I would recommend having at least one Disc Priest for any progression raid, just because of all the damage you can mitigate with bubbles. If you choose to stay Holy however, that's perfectly fine - just be prepared to go Disc offspec for LK.
For Disc, no. It would take a lot of haste to drop a single point of spellpower for Disc.
For Holy, maybe. That's only 15 haste away, depends on how much spellpower you would lose. Either way that's a tiny gear shuffle.
edit: What do you have banked for an offhand and MH? Because if you have a pair that has more SP than your current staff, you can swap weapon setups between Disc and Holy. Gem the staff with haste, and then use that for Holy, then go with the max SP 1h + oh for Disc.