I play dk since wotlk as main, and i always test stats once in a while to see if they actually gained any improvements, and haste has been an issue on this server since the beginning of MOP, in cata was top stat after strenght, but in MOP has a considerable decrease in performance. Mastery here for dk's top it in pvp and pve(i play hybrid pvp/pve), tests has been positive so far all the times although i tried to stay skeptical at first as being used with haste, till i realized that mastery outperforms haste. According to my pvp experience it does a better job in 2v2 but also in 1v1, there is no use of haste when ure constantly cced and avoided, but with mastery ur pet does higher damage while ure being keept on distance, plus ur dots do more damage as well, at which point what's most important is how u manage ur healing while being kited or kite ur adversary. Haste should be more for pve or stable close encounter, which is too complicated on an xpack where wars damage and other classes cc's are a nightmare. Example being mages and locks endless cc's, or even rogues which can kill u in one or two consecutive sessions of combos, stuns and vanishes without even giving u the chance to react. I still hope dk's will get better in the future, because so far its ridiculous that none has reached top charts, its pure humiliation of a class, i simply won't accept this, and if this is the final verdict for us, then MOP is most certainly a lost cause for dk players.