For all the cheese fans out there, this is about to get gouda.
All the top dk's I saw were stacking mastery. also enchanting mastery. I see the valid argument that Versa can sometimes trump mastery for a dk situationally.
Mastery for Dk's increases the amount of Frost dmg a DK does.
we know what versa does.
Hoochella: top dk was sitting around 57% mastery and 8% Versa ( 8%dmg ^ 4% dmg reduc)
Our fearless leader was sitting 36% mastery and 14% versa (14% dmg ^ 7percent dmg reduc)
Hooch is doing 40% more frost dmg to Vice's 20%.
Hooch is only losing 3% dmg reduc, and overall dmg by 6%.
That being said you have too look at the way that Dk's optimally deal dmg.
With the buff to howling blast and frost strike and the relative nerf to Obliterate. Frost dmg is the best way for dk's to not only deal dmg but to also be more rune efficient.
Howling blast = 1 frost rune (100% AP deals dmg in frost)
frost strike = 40 runic power (80% AP deals dmg in Frost)
obliterate = 1 frost 1 unholy ( 215% physical dmg) also has proc to increase FS and HB's dmg.
Obliterate costing 2 runes and having a chance to pro HB and FS to do more dmg as well as free makes it usable.
however the stacking of mastery increases your HB dmg and FS dmg without a severe drop in Obliterates dmg. Above u see Hooch's obliterate will hit less, although his HB and FS will hit significantly Higher.
On top of those two spells hitting harder, they add a necrotic plague and chill blains HB is AOE and FS is Single target.
Nercrotic plauge hits for 80% physical dmg as well as 20% frost dmg.
This makes blood strike a more viable part of your rotation while Obliterate is used only when Obliterate itself procs or to fill empty time.
If we are looking at the way Dk's go defensive in order to survive, they go blood (30% armor ^ 20% stam ^ 10% dmg reduction). DPs rotations doesnt change all that much (maybe more blood strikes depending on the situation), but overall dmg does not drop significantly besides you rely more on runes than runic power.
On to talents. Plague leech or Unholy Blight.
If u are running Mass grip Unholy blight.
If your are running desecrated ground plague leech.
while running unholy blight and mass grip ur burst dmg has the chance to peak at around 75k while only 60k with plague leech.