I'll spec out for the items that have Piety and if both Ironworks and Dread has Piety, then Det --> Crit --> Accuracy --> Spell Speed are my order of preferences.

I've never found an instance where Spell Speed was a make or break on anything. This game is strictly about learning rotations and timing when you can cast a heal or have to move. I've specced both full spell speed and full det/crit and I personally enjoy the det/crit. I never rely on a crit, but man is it nice when it comes.