Something I have not seen crop up a lot in these forums, but is nevertheless true, is that interrupts are NOT necessarily detrimental to the relative DPS of the black magic buff vs spell power (or other proc vs static calculations). It is true that haste suffers from the random interrupts that don't allow an extra spell cast to finish, leading to the recent posts regarding static spell power being better for most interrupt fights. However, if a significant interrupt phase occurs (think submerge for acidmaw/dreadscale in beasts or all the way back to dancing on heigen), this gives the internal cooldown on a proc like black magic time to reset. Thus, if the proc was 15 s with a 45 s internal cooldown, in the extreme case where you move for 30 secs and cast for 15, the proc would have 100% uptime essentially, making it far superior to static spell power. More realistically, lets say you move for 10 seconds out of every 45, instead of using the calculation of 15/45 * haste bonus to estimate the average haste benefit, we would do the calculation 15/35 * haste bonus, giving a much bigger effective increase. It is true that you risk having your haste bonus cut short if it procs 5 secs before the movement phase, for instance, but probability is in your favor that it will be available at the period just after the movement phase, due to a large chance the cooldown resets during the phase.