Topic Question about Demonology
Mastery is bad for Affliction, but Haste is passable for Demo.
It's fine on warmaster :)
The 10% will exceed anything switching specs and reforges would do, especially if you run ranged heavy. Just play what you like and adapt your spec as much as possible to the fight at hand. Ofc none of that applies if you are super human min/max'er and at the pointy end of progression raiding but hey ho that philosophy has always worked for me.