likewise, for arcane simple theory craft shows exactly how effective that mastery can be at current levels. Reforging haste into mastery with my findings showed the dps increase to be nearly 1.2k (which considering I'm losing a stat, is a heavy amount of gain)

Further testing onto a target dummy and I'm still capable of selfbuffed 13k dps sustained (over hours of attempts) as opposed to being just south of 12k

Granted I couldn't support evidence without boring the pants off of everyone (except you Mr. Belt, you're not wearing any) it seems that mastery weight is much higher for arcane than haste, and likewise the new mechanic for mastery places a lot of emphasis on crit over haste (both increase damage, but faster casts = less man = less bonus from mastery, as opposed to bigger numbers more often). More so, I managed to reforge nearly 10% haste ( a very sizeable number) into roughly 6.5ish points of mastery rating. At 80, mana management is nearly redundant (as you reach higher gear levels) even during our burn phases with the changes to mage armor.

I think as far as reforging goes, @80 mastery is a contender with hit (as after a % of hit, mastery will yield a higher dps increase, which is roughly 12%), however, at 85 as we'll see it from gear more often, we'll most likely reforge spare stats into hit (to avoid needing a new piece of gear, or regemming) or more so on the crit/haste front, as certain trees value one over the other.