Mighty spellpower or Black Magic

The Black Magic enchant for weapons will be changed with patch 3.3, and will now give the weapon a chance to proc 250 haste rating for 10sec. Could this be an alternativ to Mighty spellpower?

I tested it on the PTR last night and found that it have a 35sec internal cooldown and ~50% proc-chance. This means we can expect it to proc approx. every 35 + 1,5/0,50 = 38,0sec, which result in 250 x 10/38 = 65,8 avg. haste rating.

Using DEP-values at 1,509 for spellpower and 1,432 for haste rating, this gives the following output for the two enchants.

Mighty spellpower:
63 x 1,509 = 95,1 dps

Black Magic:
65,8 x 1,432 = 94,2 dps

The two enchants seems on pair with eachother, but in my opinion a static spell power-buff is prefered over a proc-based haste-buff. I will test it again, when patch 3.3 goes live.

Change to Elemental Mastery

They are changing Elemental Mastery with patch 3.3 from giving 15% crit for 15sec to 15% haste for 15sec.

15% crit was equal to 15 x 45,91 = 689 crit rating
15% haste is equal to 15 x 32,79 = 492 haste rating

With Elemental Mastery popped every 3 min and with DEP-values for crit and haste rating at 0,761 and 1,432 - I will expect a 15/180 x (492 x 1,432 - 689 x 0,761) = 15,0 dps upgrade

It's also worth to note, that this upgrade will also increase the value of the Tier 10 2-piece bonus, since Elemental Mastery will be used around twice as much.