This whole thing spawned because of an argument I had with someone on Wowhead forums about tanks using rend. It got me to re-download the threat add-on Satrina used in the groundbreaking "3.0 Threat Values" thread.
Note that I wiped out my talent trees because Damage Shield, Deep Wounds, Enrage Procs, and Shield Spec Procs were annoying to sort through. Also note that all of the "threat" values are divided by 207.35 defensive stance modifier to "normalize" the value, as in the original thread.
I'll start with a few other abilities before I get into Devastate:
Bloodrage:
0 threat
Pop Bloodrage, gain 20 rage
10000 threat
11037 threat
12074 threat
12148 threat
Initial 20 rage is not modified by stance (5 threat per rage * 100% modifier). The extra 10 rage from ticks are affected by stance's 207.35% modifier (5 threat per rage * 207.35% modifier).
Improved Bloodrage Talent:
0 threat
Pop Bloodrage, gain 30 rage
15000 threat
16555 threat
18110 threat
19665 threat
So the way Improved Bloodrage works is you get 30 rage plus 15 over 10 seconds. You actually get 1.5 rage per second, which is why this is showing 7.5 threat per tick. Again, Initial 30 rage is not modified by stance, but the 15 rage from ticks is modified by the 207.35%. (5 threat per rage gained)
Sunder Armor with 2404 Attack Power
1191065 threat
Sunder Armor
Melee 595
1413965 threat
1075 threat. Minus melee swing is 480 threat, 360? from sunder + 120 from AP (5% of 2404)
Sunder Armor with 2396 Attack Power
3606149 threat
Sunder Armor
Melee 329
3773687 threat
808 threat. Minus 329 melee swing is 479 threat. 360? from sunder + 119 from AP (5% of 2396)
Sunder Armor with 2300 Attack Power
1048919 threat
Sunder Armor
1144409 threat
475 threat. 360? from sunder + 115 from AP 5% of 2300.
Sunder Armor with 3690 Attack Power
562540 threat
Melee - 1298
Sunder Armor
944478 threat
1842 threat, minus 1298 melee is 544 threat. 360? from sunder and 184 from AP (5% of 3690)
[So it looks like the innate threat from Sunder Armor is 360 + 5% AP now]
Shield Specialization:
The 5 rage gained from Dodge/Parry/Block an attack does 5 threat per rage (25 threat per D/P/
which is not modified by stance.
Improved Defensive Stance
Every time the enrage effect occurs, even if it is just refreshing the buff, you gain 1 threat, which IS modified by stance.
Shield Slam and Revenge:
I didn't write down any of the data, but verified that they are still Damage + 770 and Damage + 121 respectively.
Now with that out of the way, here's a bunch of Devastate data. I'll start off with a summary. I was trying to verify that Glyph of Devastate still worked as it did pre-3.2, that is doubling the threat that is added from the 5% AP. What I found is that the "bonus" threat from Devastate seems to change depending on how much attack power you have; the more AP you have the less percent bonus you get. Note however that at a "baseline" of around 2500 AP (my unbuffed AP), I was getting ~17% AP bonus as threat, NOT the 5% from pre-3.2. And I also verified that the threat does not change based on the number of sunders on the target, and Glyph of Devastate does still double the extra threat.
What I need is help in figuring out how this scales. Maybe I'm missing something simple. Anyway, here are my findings:
Unglyphed Devastate:
1256 Attack Power
725516
Sunder Armor
Devastate - 551
917937
928 threat, minus devastate damage is 377 extra threat (30% of 1256 AP).
1082572 threat
Sunder Armor
Devastate - 690
1303815
1067 threat, minus devastate damage is 377 extra threat.
2422 Attack Power
757243
Melee - 345
Sunder Armor
Devastate - 1243
1176820
2024 threat. Minus 345 melee is 1679, minus devastate damage is 436 extra threat. 436 is 18% of 2422 AP.
1336579 threat
Sunder Armor
Devastate - 731
Melee - 342
1649471 threat
1509 threat. Minus 342 melee is 1167, minus devastate damage is 436 extra threat.
1725776 threat
Melee - 367
Sunder Armor
Devastate - 911
2081174 threat
1714 threat. Minus 367 melee is 1347, minus devastate damage is 436 extra threat
2524 Attack Power
155928 threat
Melee - 437
Sunder Armor
Devastate - 644
471514 threat
1522 threat, minus 437 melee and 644 devastate is 441 extra threat (17.4% of 2524 AP)
3430 Attack Power
425274 threat
Melee 464
Sunder Armor
Devastate - 832
794771 threat
1782 threat, minus 464 melee and 832 devastate damage is 486 extra threat, 14% of 3430 AP...
3980 Attack Power
778600
Melee - 605
Sunder Armor
Devastate - 1212
1272300
2381 threat, minus 605 melee and 1212 devastate is 564 extra threat, 14 % of 3980 AP.
Devastate using Glyph of Devastate:
2524 Attack Power
293814 threat
Sunder Armor
Sunder Armor
Devastate - 1384
Melee - 346
835411 threat
2612 threat, minus 346 melee and 1384 devastate is 882 extra threat (35%% of 2524 AP, twice the extra threat of unglyphed)
912753 threat
Sunder Armor
Sunder Armor
Devastate - 1080
Melee - 439
1410600
2401 threat, minus 439 melee and 1080 devastate is 882 extra threat.
2176758 threat
Melee - 363
Sunder Armor
Devastate - 1249
2693888 threat
2494 threat, minus 363 melee and 1249 devastate is 882 extra threat.
1863107 threat
Sunder Armor
Devastate - 1250
2305176 threat
2132 threat, minus 1250 devastate is 882 extra threat.
[Note these last two data points are with 5 stacks of sunder on the mob, thus only one listing of Sunder Armor being applies, but it still gives double the unglyphed threat]
So given all of that, I'd ask if someone else can do some research of their own, varying the amount of attack power they have. I'm pretty sure the bonus is not modified by weapon speed, as I tried some tests with both 1.6 and 2.6 speed weapons.
Once we can nail down exactly how the bonus threat from Devastate works, this may have some pretty big implications on tanking. If Glyphed Devastate is doing Damage + ~30% Attack Power as threat when you are raid buffed, that's 1500 in bonus threat alone.