Best weapons enchant comboFollow

I haven't seen any hard numbers on Black Magic since it was changed to grant haste in offensive spell cast. My current build is gemmed exclusively for haste with the only exceptions being expertise gems where needed to maintain 140 rating. Fully raid buffed my AP is something like 6.3k, and then I get boosts to AP throughout an encounter from Berserking x 2 and the proc on Blood of the Old God (another 1k or so).

According to what I've read, Black Magic has a chance to grant 250 haste rating on offensive spell cast, which would work out to about 4-5% melee haste for an enhancement shaman. I can't find any information (after an albeit superficial search) on the duration of that haste buff or PPM on the enchant.

If you're gemming for AP and Agility, the added haste might be more beneficial to you. In my case, given that I'm already coming close to 700 haste rating (just over 27% melee haste), I'd want to sim both options and compare before I'd offer anything concrete. I personally don't plan on changing OH enchant to Black Magic atm, but that could change in light of compelling evidence that it would be a better option.