[Shadow Priests] Haste

A guild mate asked me a question about haste. Now most information I've been able to glean via Google and other reputable sources (Elitist Jerks and shadowpriest.com) tend to have very little information on haste for Shadow Priests.

The original question he wanted was the coefficient for haste to DPS. Unfortunately, that information is nowhere to be found meaning that we have to run tests for figuring this out. 

I'm showing that most priests are stacking haste well into the mid 800s (Source here) though there seems to be a large amount of crying by the Shadow Priest community as a whole about how they did not get Shadow Word: Pain to be effected by haste as well.

Though most are not overly concerned about SW:P, but more about their overall DPS, and how reliant their rotations are on being exact to output the optimum DPS required for the current raiding environment we have today.

Right now, I'm even seeing people saying that whether or not one goes for haste over crit or vice versa is dependent on play style. 

I suppose that could potentially be true with any class, because as a discipline priest I tend to stray away more from stacking MP5 or Spirit, and more towards INT giving me more crit and a huge mana pool, while others are stacking MP5 for fear of running OOM.

Really, there's no right amount of haste currently that reflects a mechanic imposed cap, so I would say that you're probably best off with having your haste as high as it could be without sacrificing any other important stats.