Pushing Haste beyond 40% continues to grant improvement. My tests have always shown even 100% Haste continues to show reasonable DPS increase over 99%. That said, around the 40% mark you may begin to gain more from 1% additional Mastery or Crit rather than 1% Haste. So if you had a choice of stats, Haste might no longer be your first pick. Some people erroneously call this a softcap, when capping is nowhere involved.
Then again, Haste might still be your best stat. Follow your Sim.
As for Divine Purpose, my tests do not show a random takes-a-GCD ability becoming superior at higher levels of Haste. In SoO gear, we tend to have fewer free GCD, especially with extra DS proccing here or there, not more. SW also benefits from Evil Eye - shorter CD on AW, which still lasts 30 seconds, means greater up-time, which means DPS boost. Plus the standard 'on demand' vs 'random proc' comparison.
I suspect the DivPurp suggestion is anecdotal (they tested on a dummy and liked their results), rather than mathematical. 4 piece DS can proc DivPurp and DivPurp can proc 4 piece. So you could occasionally get streaks of many TV/DS in some variety. It is improbable, and if it did occur, could easily be during a movement/transition/can't-hit-boss timeframe (i.e. entirely lost).
I'll end with my usual caveat - it's always possible some specific set of gear shows unusual results on simulations and that a non-typical talent is ideal. I continue to suggest folks run their own tests and follow personal results rather than blindly follow a generic guide.
Edited by Exemplar, 28 May 2014 - 12:56 PM.