Originally Posted by
Dust45
This. The only spells that a Holy Priest should be casting on a regular basis that will benefit (aside from strict throughput) from haste are Light Well and, maybe, a few renews. Holy Word Sanctuary is basically useless. Renew isn't a terrible spell, great for movement, of course, but it simply doesn't pack the oomph that your other spells do. You should be using (provided healing is needed) Circle of Healing, Cascade/Halo/Divine Star (switch talent for each fight as needed), Prayer of Mending, and, if in Serenity for some reason, Holy Word: Serenity on cooldown. You should fill the rest of your time with Prayer of Healing and, maybe, a few greater heals if necessary (doubtful with the pally there).
Everything else is just for emergency/lots of movement healing. (Obviously, you should still use your big CDS whenever necessary as well).
In a word, everything benefits from Mastery but not everything benefits from haste. Spirit and Mastery for the win in every reforge/gem.