Because i couldnt find any comparisons i thought i would do some theorycraft (as an aspiring arms/prot offtank). Scroll to the end of the post for conclusions.
Assuming you are initially following a rotation of
revenge, sunder, sunder, sunder --> repeat
What is the difference between adding heroic strikes, or replacing a sunder with a mortal strike. I'm going to ignore defiance and def stance as they effect both equally.I'll also ignore armor and crits for now. I'll also assume a 90 dps weapon and 1000 attack power.
2.6 speed weapon
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instant attack damage = (90 * 2.6) + [(1000/14) * 2.4] ~= 405
none normalised attack damage = [90 + (1000/14)] * 2.6 ~= 419
ms threat ~= 405 +210 = 615
ms / sunder threat difference ~= 615 - 301 = 314
ms additional threat per second ~= 314/6 ~= 52.3~
ms additional threat per rage 0 imp sunder ~= 314/(30 - 15) ~= 20.9
ms additional threat per rage 1 imp sunder ~= 314/(30 - 14) ~= 19.6
ms additional threat per rage 2 imp sunder ~= 314/(30 - 13) ~= 18.5
ms additional threat per rage 3 imp sunder ~= 314/(30 - 12) ~= 17.4
hs additional threat = 176(thats the extra dmg) + 196(thats the additional threat) = 372
hs additional threat per second = 372/2.6 ~= 143
white hit would have given you = (7.5 * 419 / 274.7 + 3.5 * 2.6) / 2 ~= 10.26
this assumes
http://www.wowwiki.com/Formulas:Rage_generation is correct
hs threat per rage 0 imp hs = 372/(10.26+15) = 14.72
hs threat per rage 1 imp hs = 372/(10.26+14) = 15.3
hs threat per rage 2 imp hs = 372/(10.26+13) = 16
hs threat per rage 3 imp hs = 372/(10.26+12) = 16.7
1.6 speed weapon
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instant attack damage = (90 * 1.6) + [(1000/14) * 2.4] ~= 315
none normalised attack damage = [90 + (1000/14)] * 1.6 ~= 258
ms threat ~= 315 +210 = 525
ms / sunder threat difference ~= 615 - 301 = 224
ms additional threat per second ~= 244/6 ~= 37.3~
ms additional threat per rage 0 imp sunder ~= 244/(30 - 15) ~= 16.2
ms additional threat per rage 1 imp sunder ~= 244/(30 - 14) ~= 15.25
ms additional threat per rage 2 imp sunder ~= 244/(30 - 13) ~= 14.46
ms additional threat per rage 3 imp sunder ~= 244/(30 - 12) ~= 13.6
hs additional threat per second = 372/1.6 ~= 232.5
white hit would have given you = (7.5 * 258 / 274.7 + 3.5 * 1.6) / 2 ~= 6.3
hs threat per rage 0 imp hs = 372/(6.3+15) = 17.56
hs threat per rage 1 imp hs = 372/(6.3+14) = 18.32
hs threat per rage 2 imp hs = 372/(6.3+13) = 19.26
hs threat per rage 3 imp hs = 372/(6.3+12) = 20.32
Summery
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A quick thought on armor reduction of the boss, comparative threat values should scale the same, however hs should decrease in efficiency slower as you wont be gaining as much rage for a white hit.
with a 1.6 speed weapon and infinite rage you can put out an additional ~269.8 tps with hs and ms
with a 2.6 speed weapon and infinite rage you can put out an additional ~195.3 tps with hs and ms
Fast weapon wins for tps in infinite rage environment.
For a rage limited environment, heroic strike is more efficient if you have a fast weapon and ms is more efficient if you have a slow weapon.
Surprisingly though if you have 3 imp hs, hs with a fast weapon is always either more efficient or just as efficient as mortal strike.
I'm sure i've made lots of stupid mistakes, and i've been very liberal with rounding, so feel free to correct me on anything/mock my assumptions/spelling/face.
Current Advice
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For the time being, get a fast weapon, spec imp hs and use
revenge, sunder, sunder, sunder --> repeat
throwing in heroic stikes when you have the rage. Only ms if you have to much rage to spend on heroics AND your mortal strikes hit for higher than 301 (sunders threat).
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