Running the numbers, there appears to be a direct correlation between haste and an increase in DPS. ie....a 10% increase in haste = 10% increase in DPS.
This of course doesn't not take into consideration non-numerical data such as reaction times and times required to be out of combat to do something else (move out of a damage aura, cleanse, bandage, etc) or how itemization affects things. What do you have to give up to get haste.
Numerically, it appears that 15.7 haste = 1% haste based on 50% requiring a rating of 785.
Numerically, it appears that even with one source of cooldown mana regen, the likelyhood of going OOM at an inopportune time in the fight is not affected assuming a significant portion of the raid DPS has similiar haste rating. The more varied the DPS haste ratings are, the more likely with the higher of your own rating of going OOM at an inopportune time is greatly increased if you have only one source of cooldown mana regen (that is potions, innervates etc).
Assuming damage output from the encounter does not change with the overall haste rating of your party, haste ratings for healers is not affected in the same way for the same effect. If the damage taken by a tank is 10,000 dps, then healers need to heal said tank for 10,000 hps. If the healing core is already adequate, haste rating will benefit mana regen more then amount healed. Because if you can heal that 10,000 now with zero haste, having 10% haste doesn't change this, it does get you regening mana faster in your mana regen model. Which is an interesting concept in that healing classes dependant on spirit for mana regen can get out of the 5 second rule quicker. Is it signifiant, it could equate to an extra heal or two every minute. I haven't run the numbers for healing yet myself, I can't wrap my head around the variables yet.
The question then becomes:
- Would we want to increase haste rating by a predictable amount (ie...drums)?
- Require a set amount per raider? And if so, at what cost? Haste on items takes itemization away from other area's and that will skew numbers. If getting 10% more haste = 10% less +damage you have gained nothing.
- Is it enough to have one set of drums per group for extra boosts through out the fight?
- How would one strategize the use of heroism, powerinfusion, icy veins through out the raid?
- Even if the raid leaders set a goal of: Two groups under the affects of haste per minute, then you've increased overall DPS over what we have now.