I saw that you were posting about t7, so its safe to say you're playing on frostmourne. While learning to manage mana better with rapture is a good strategy for t10, especially due to how the fights are structured, using dmc + gemming intellect is a very viable (and in my opinion the optimal) strategy on Frostmourne at the moment. While t7 fights are piss easy and short, Ulduar fights are going to be much longer and healing intensive. Additionally, there aren't always mechanics as perfect as infest on LK for maximizing rapture gains as a disc. I would advise keeping the darkmoon card for Ulduar, paired with illustration if you can get it, or forethought talisman otherwise.