So most people reforge haste as frost, however I have been thinking about that and it just doesn't make sense. Yeah, you attack faster which gives you a higher chance. And yeah, runes regenerate a little faster. But honestly, when is there ever a situation where that enemy player just sits there and lets you hit him?
With that being said, I have been experimenting with reforging stacking critical strike and mastery instead. It has proven quite effective. If i get a string of obliterate crits, I can drop someone in the blink of an eye. And if they survive that, then the mastery comes in handy, howling blast crits for 40-50, maybe 60k.
Just some food for thought.