My current, and final RAF group has two priests, once shadow, and one discipline (plust 3xWarlocks). The Disc priest is the healer, and does fine, although healing a lock group is pretty easy, and I'm very low level, only Lv45, and haven't run any instances.

My last RAF group, (1xPalyy, 1xHoly Priest, 3xFire Mage) that I leveled to 60 just prior to this patch, placed a bit more demand on the healer, and the Holy priest DID seem to be stronger than my disc priest.

Since you don't have to be Holy anymore to get Holy Nova, the difference isn't all that great, and I like being able to put the Spirit buff on the group, that now includes a bonus to spell damage. Only time will tell whether I'll miss circle of healing, from the Holy talent tree!