Saying you don't need movement speed is simply wrong. You do. If you don't understand/know why you just haven't gotten far enough into the heroic modes yet.
If you play affliction you should probably go all out haste, in your gear. If 320 int > 480 haste is best found out by simming yourself, I reckon they'll be equal.
Imo, with your trinkets and because you're still progressing, you should go demonology.
You can pull huge numbers as affliction, but it depends crazy heavily on your trinket procs. I vary from 280k to 150k based on procs. Did I mention this game is well made.