Originally Posted by Notoris

According to the stat values stated in the Key Stats section the value of haste (1.95) greatly exceeds the value og spell power (1.77) for early tier10 and ICC related gear. Knowing that these stat values are are only a rough guide line and are subjects to change as your gear changes it still indicates that haste is pretty much what you want.
I noticed that in the enchants section the Enchant Weapon - Black Magic is not commented yet.
This one adds a 250 haste rating for 10 secs. when it procs. Proc. chance is 35% and has an internal cd of 35 secs. In practice this means that the haste buff is up about 25% of the time giving an average of 62-63 haste during a suitable long fight.
Now compared to the normal Enchant Weapon - Mighty Spellpower the Black Magic should actually be better (63*1.77~112) <(63*1.95~123).
Worth noting is that as with any other ability with a proc chance you can't rely on it to be up the best possible moment (when you got a 10 sec. window of pure nuking) and it might proc right when you are about to move away from Malleable Goo.

I haven't tried it out myself yet but if anyone could confirm or reject that Black Magic is actually giving better results than the standard 1H Spell Power enchant please comment.

N.B. If you got a staff use Enchant Staff - Greater Spellpower ofc.