A disc priest should have a PW:Shield that lasts slightly longer than the other 2 specs IMO. I really wish they would make the talent Soul Warding also add 2/4 secs to the duration of PW:Shield along with reducing the cd. I don't think it's too much to ask for and adding 4 secs won't make it OP while making the life of a Disc Priest a little bit better.