Ugh, OK well sorry if this post is a little sloppy, I just wrote out a novel and accidentally lost it as I went to preview the post before submitting it. I wanted to post this a day or two ago, but the delay between registering and posting delayed that. So I'm not really in high spirits to write it all out again.
Now then, on the topic of Webbed Death being the best offhand, a week or two ago I simulated a bunch of offhands myself, and came to the same conclusion. However, since then I've refined my process, and though I little out of the box and came up with something much more interesting.
As a prefix to these results. They were all calculated with the same gear, spec, gems, glyphs. Keep in mind that the glyphs I currently have are Windfury, Flametongue, and Stormstrike. I started by taking off my weapons and input my stats without them. I then went and adding the stats for the weapons in myself by hand. Yes, I remembered to calculates stats make and the effect of ap on spellpower.
Additionally, my gear isn't overly good. Up until this week I haven't really done any 25man content. I do however have pretty much everything you would want from 10man raiding. Unfortunately, as I did all the tests with the same setup up, some combination do fall below the spell hit cap. However, it doesn't really change the end result of what I'm trying to show. So bear with me.
I'll write some notes before each log, and summaries the results below if you don't care about the logs themselves.
Vanilla 'best'
[Calamity's Grasp]/WF &
[Angry Dread]/FT 4881.16dps

MH:
miss 6795090 11.09%
dodge 919525 1.50%
glancing 15320141 25.00%
hit 8261107 13.48%
crit 29991914 48.94%
MH Windfury:
procs/hits 15.21%
procs/swings 13.53%
miss 0 0.00%
dodge 287765 1.50%
hit 9638347 50.34%
crit 9219888 48.16%
MH Storsmtrike:
miss 0 0.00%
dodge 142224 1.50%
hit 4780729 50.37%
crit 4568173 48.13%
OH:
miss 7062433 11.08%
dodge 955548 1.50%
glancing 15940362 25.01%
hit 8576355 13.45%
crit 31207534 48.96%
OH Flametongue:
miss 611092 0.80%
hit 43406970 56.72%
crit 32511588 42.48%
OH Stormstrike:
miss 0 0.00%
dodge 140458 1.50%
hit 4701739 50.29%
crit 4506705 48.21%
Earth Shock:
miss 102293 0.80%
hit 7260217 56.72%
crit 5436780 42.48%
Lava Lash:
miss 0 0.00%
dodge 176701 1.50%
hit 5899806 50.11%
crit 5697149 48.39%
Lightning Bolt:
miss 96727 0.80%
hit 6887951 56.73%
crit 5157457 42.48%
Lightning Shield:
miss 82803 0.80%
hit 10301236 99.20%
crit 0 0.00%
Maelstrom Weapon:
PPM 44.89
flurry uptime 89.52%
unleashed rage uptime 0.00%
elemental devastation uptime 76.76%
elemental oath uptime 0.00%
mh enchant uptime 34.55%
oh enchant uptime 30.68%
trinket1 uptime 20.53%
trinket2 uptime 18.03%
totem uptime 47.14%
set bonus uptime 0.00%
metagem uptime 0.00%
MRPS without overregen
mana regen 0.00 0.00%
mp5 16.76 13.94%
replenishment 35.15 29.23%
unrelenting storm 0.00 0.00%
judgement of wisdom 28.06 23.34%
shamanistic rage 40.27 33.49%
mana potion 0.00 0.00%
misc potion 0.00 0.00%
DPS PPM MPS
white 1551.53 31.79% 83.35
windfury 627.69 12.86% 6.38
flametongue 496.25 10.17% 51.02
stormstrike 267.92 5.49% 6.33 34.86 26.41%
lava lash 151.04 3.09% 7.85 15.74 11.92%
searing totem 298.37 6.11% 1.00 4.82 3.65%
earth shock 566.74 11.61% 8.53 30.51 23.11%
lightning bolt 743.16 15.23% 8.09 46.07 34.90%
lightning shield 178.47 3.66% 0.77 0.00 0.00%
DPS 4881.16
MPS 132.01
MP2min 15840.76
MRPS 139.02
Out of mana time 0.08%
elapsed simulation time: 25000.00h
elapsed real time: 90.47s
simulation speed: 994826x
Next, the recent 'proposed best'. I realise I had stated earlier that Webbed Death came out ahead of Angry Dread, but that was using my gear from a week or two ago. Since then I had replaced a fair amount of hit rating, and I suspect that is the major difference. Luckily, this isn't really what I'm trying to prove anyways, so it doesn't much matter.
[Calamity's Grasp]/WF &
[Webbed Death]/FT 4860.64dps

MH:
miss 6836320 11.22%
dodge 914908 1.50%
glancing 15229615 25.00%
hit 8224680 13.50%
crit 29715523 48.78%
MH Windfury:
procs/hits 15.25%
procs/swings 13.54%
miss 0 0.00%
dodge 286225 1.50%
hit 9625068 50.50%
crit 9149141 48.00%
MH Storsmtrike:
miss 0 0.00%
dodge 141822 1.50%
hit 4771435 50.48%
crit 4537990 48.01%
OH:
miss 12765703 11.21%
dodge 1706407 1.50%
glancing 28459387 25.00%
hit 15322060 13.46%
crit 55587652 48.83%
OH Flametongue:
miss 1106565 0.92%
hit 67899454 56.48%
crit 51217862 42.60%
OH Stormstrike:
miss 0 0.00%
dodge 139120 1.49%
hit 4691158 50.39%
crit 4479147 48.11%
Earth Shock:
miss 118620 0.92%
hit 7269872 56.47%
crit 5485547 42.61%
Lava Lash:
miss 0 0.00%
dodge 178190 1.50%
hit 5959049 50.23%
crit 5725428 48.26%
Lightning Bolt:
miss 105815 0.92%
hit 6496977 56.51%
crit 4894156 42.57%
Lightning Shield:
miss 116087 0.92%
hit 12565008 99.08%
crit 0 0.00%
Maelstrom Weapon:
PPM 42.18
flurry uptime 87.33%
unleashed rage uptime 0.00%
elemental devastation uptime 75.99%
elemental oath uptime 0.00%
mh enchant uptime 34.43%
oh enchant uptime 25.95%
trinket1 uptime 20.87%
trinket2 uptime 18.81%
totem uptime 47.39%
set bonus uptime 0.00%
metagem uptime 0.00%
MRPS without overregen
mana regen 0.00 0.00%
mp5 16.81 14.02%
replenishment 35.26 29.41%
unrelenting storm 0.00 0.00%
judgement of wisdom 29.60 24.69%
shamanistic rage 38.21 31.88%
mana potion 0.00 0.00%
misc potion 0.00 0.00%
DPS PPM MPS
white 1540.71 31.7% 116.51
windfury 623.85 12.83% 6.35
flametongue 624.34 12.84% 80.15
stormstrike 229.30 4.72% 6.30 34.72 26.74%
lava lash 85.05 1.75% 7.91 15.94 12.28%
searing totem 292.26 6.01% 1.00 4.83 3.72%
earth shock 561.74 11.56% 8.58 30.71 23.66%
lightning bolt 689.63 14.19% 7.66 43.64 33.61%
lightning shield 213.76 4.4% 0.94 0.00 0.00%
DPS 4860.64
MPS 129.83
MP2min 15579.92
MRPS 134.09
Out of mana time 0.07%
elapsed simulation time: 25000.00h
elapsed real time: 103.22s
simulation speed: 871940x
Ok, here is where things get a bit interesting. I thought that if we were trying to maximize flametongue damage through weapon speed. Why not just go all out with it and see what happens?
Remember to keep in mind i'm still using the Windfury Glyph in this test even though it does me no good!
[Torch of Holy Fire]/FT &
[Webbed Death]/FT 5032.07dps

MH:
miss 9884476 11.21%
dodge 1324895 1.50%
glancing 22030512 24.99%
hit 13160042 14.93%
crit 41743051 47.36%
MH Flametongue:
miss 793046 0.92%
hit 47378679 54.97%
crit 38019837 44.11%
MH Storsmtrike:
miss 0 0.00%
dodge 140705 1.50%
hit 4883475 51.96%
crit 4374482 46.54%
OH:
miss 12725280 11.21%
dodge 1703966 1.50%
glancing 28394010 25.00%
hit 16962031 14.94%
crit 53771349 47.35%
OH Flametongue:
miss 1106742 0.92%
hit 66117594 54.97%
crit 53056815 44.11%
OH Stormstrike:
miss 0 0.00%
dodge 139763 1.51%
hit 4801561 51.86%
crit 4316633 46.63%
Earth Shock:
miss 119952 0.92%
hit 7165713 54.96%
crit 5752566 44.12%
Lava Lash:
miss 0 0.00%
dodge 182666 1.50%
hit 6314589 51.68%
crit 5720978 46.82%
Lightning Bolt:
miss 92252 0.92%
hit 5518550 54.96%
crit 4430227 44.12%
Lightning Shield:
miss 119113 0.92%
hit 12869673 99.08%
crit 0 0.00%
Maelstrom Weapon:
PPM 35.94
flurry uptime 84.69%
unleashed rage uptime 0.00%
elemental devastation uptime 75.57%
elemental oath uptime 0.00%
mh enchant uptime 23.35%
oh enchant uptime 26.01%
trinket1 uptime 20.91%
trinket2 uptime 18.83%
totem uptime 47.99%
set bonus uptime 0.00%
metagem uptime 0.00%
MRPS without overregen
mana regen 0.00 0.00%
mp5 19.92 19.61%
replenishment 35.79 35.23%
unrelenting storm 0.00 0.00%
judgement of wisdom 30.46 29.98%
shamanistic rage 15.42 15.18%
mana potion 0.00 0.00%
misc potion 0.00 0.00%
DPS PPM MPS
white 1367.91 27.18% 134.47
flametongue 1371.70 27.26% 137.65
stormstrike 151.90 3.02% 6.27 34.52 27.73%
lava lash 85.00 1.69% 8.15 16.45 13.21%
searing totem 376.65 7.49% 1.00 4.83 3.88%
earth shock 670.68 13.33% 8.69 30.66 24.63%
lightning bolt 745.07 14.81% 6.69 38.02 30.54%
lightning shield 263.15 5.23% 0.96 0.00 0.00%
DPS 5032.07
MPS 124.49
MP2min 14938.61
MRPS 103.91
Out of mana time 0.02%
elapsed simulation time: 25000.00h
elapsed real time: 107.27s
simulation speed: 839043x
Well then, we should probably check to see if it's just the torch that is giving us that huge boost.
[Torch of Holy Fire]/FT &
[Angry Dread]/FT 4870.93dps

MH:
miss 9688635 11.09%
dodge 1311894 1.50%
glancing 21839892 25.00%
hit 13899140 15.91%
crit 40607093 46.49%
MH Flametongue:
miss 684424 0.80%
hit 46607854 54.42%
crit 38359852 44.79%
MH Storsmtrike:
miss 0 0.00%
dodge 142609 1.51%
hit 4980297 52.71%
crit 4325708 45.78%
OH:
miss 6943263 11.08%
dodge 938876 1.50%
glancing 15657857 25.00%
hit 9974172 15.92%
crit 29126094 46.50%
OH Flametongue:
miss 607611 0.80%
hit 41295767 54.41%
crit 33987362 44.78%
OH Stormstrike:
miss 0 0.00%
dodge 139473 1.50%
hit 4905892 52.72%
crit 4260640 45.78%
Earth Shock:
miss 104031 0.80%
hit 7060311 54.43%
crit 5807978 44.77%
Lava Lash:
miss 0 0.00%
dodge 181718 1.50%
hit 6379367 52.51%
crit 5586718 45.99%
Lightning Bolt:
miss 84999 0.80%
hit 5774986 54.41%
crit 4753464 44.79%
Lightning Shield:
miss 83910 0.79%
hit 10478827 99.21%
crit 0 0.00%
Maelstrom Weapon:
PPM 38.20
flurry uptime 84.96%
unleashed rage uptime 0.00%
elemental devastation uptime 77.08%
elemental oath uptime 0.00%
mh enchant uptime 0.00%
oh enchant uptime 0.00%
trinket1 uptime 20.58%
trinket2 uptime 17.99%
totem uptime 47.79%
set bonus uptime 0.00%
metagem uptime 0.00%
MRPS without overregen
mana regen 0.00 0.00%
mp5 19.87 18.03%
replenishment 35.64 32.34%
unrelenting storm 0.00 0.00%
judgement of wisdom 28.98 26.30%
shamanistic rage 25.70 23.33%
mana potion 0.00 0.00%
misc potion 0.00 0.00%
DPS PPM MPS
white 1330.32 27.31% 99.99
flametongue 1168.94 24% 107.70
stormstrike 185.70 3.81% 6.30 34.71 27.56%
lava lash 148.62 3.05% 8.10 16.18 12.85%
searing totem 373.79 7.67% 1.00 4.83 3.83%
earth shock 666.29 13.68% 8.65 30.17 23.96%
lightning bolt 784.81 16.11% 7.08 40.05 31.80%
lightning shield 212.46 4.36% 0.78 0.00 0.00%
DPS 4870.93
MPS 125.93
MP2min 15112.03
MRPS 115.28
Out of mana time 0.04%
elapsed simulation time: 25000.00h
elapsed real time: 88.89s
simulation speed: 1012487x
Finally, I had simulated what Rounced just joked about, I snickered when I came back today and saw he mentioned it....
[Torch of Holy Fire]/FT &
[Librarian's Paper Cutter]FT 4954.04dps

MH:
miss 10545094 11.86%
dodge 1334601 1.50%
glancing 22236353 25.01%
hit 13286951 14.94%
crit 41511014 46.69%
MH Flametongue:
miss 1344626 1.56%
hit 46647025 54.05%
crit 38304212 44.39%
MH Storsmtrike:
miss 0 0.00%
dodge 141530 1.51%
hit 4940564 52.54%
crit 4320981 45.95%
OH:
miss 14618399 11.86%
dodge 1849576 1.50%
glancing 30820292 25.00%
hit 18413585 14.94%
crit 57566427 46.70%
OH Flametongue:
miss 1997180 1.56%
hit 69179274 54.05%
crit 56820110 44.39%
OH Stormstrike:
miss 0 0.00%
dodge 138839 1.50%
hit 4867564 52.56%
crit 4255142 45.94%
Earth Shock:
miss 203503 1.56%
hit 7059111 54.06%
crit 5794236 44.38%
Lava Lash:
miss 0 0.00%
dodge 183474 1.50%
hit 6413201 52.32%
crit 5660353 46.18%
Lightning Bolt:
miss 155371 1.56%
hit 5402450 54.08%
crit 4432323 44.37%
Lightning Shield:
miss 209452 1.56%
hit 13203640 98.44%
crit 0 0.00%
Maelstrom Weapon:
PPM 35.74
flurry uptime 83.91%
unleashed rage uptime 0.00%
elemental devastation uptime 75.74%
elemental oath uptime 0.00%
mh enchant uptime 23.22%
oh enchant uptime 25.44%
trinket1 uptime 20.95%
trinket2 uptime 18.91%
totem uptime 47.84%
set bonus uptime 0.00%
metagem uptime 0.00%
MRPS without overregen
mana regen 0.00 0.00%
mp5 19.93 19.76%
replenishment 35.76 35.45%
unrelenting storm 0.00 0.00%
judgement of wisdom 30.42 30.15%
shamanistic rage 14.76 14.64%
mana potion 0.00 0.00%
misc potion 0.00 0.00%
DPS PPM MPS
white 1318.56 26.62% 141.45
flametongue 1387.12 28% 142.86
stormstrike 143.50 2.9% 6.27 34.54 27.80%
lava lash 73.84 1.49% 8.17 16.49 13.27%
searing totem 370.79 7.48% 1.00 4.83 3.89%
earth shock 663.36 13.39% 8.70 30.61 24.64%
lightning bolt 730.05 14.74% 6.66 37.79 30.41%
lightning shield 266.81 5.39% 0.99 0.00 0.00%
DPS 4954.04
MPS 124.25
MP2min 14910.54
MRPS 102.81
Out of mana time 0.02%
elapsed simulation time: 25000.00h
elapsed real time: 119.30s
simulation speed: 754425x
So, what are the final results?
[Calamity's Grasp]/WF &
[Angry Dread]/FT 4881.16dps
[Calamity's Grasp]/WF &
[Webbed Death]/FT 4860.64dps
[Torch of Holy Fire]/FT &
[Webbed Death]/FT 5032.07dps
[Torch of Holy Fire]/FT &
[Angry Dread]/FT 4870.93dps
[Torch of Holy Fire]/FT &
[Librarian's Paper Cutter]/FT 4954.04dps
Oh dear. A BoE blue the second best offhand? Well hold on now! If you noticed from the simulations I actually have almost a 1.6 miss rate with spells using the Librarian's Paper Cutter. With some poking around with my stats (hit rating mostly) you can actually get it's dps higher than Webbed Death. As my gear isn't that good, it is actually quite possible that it IS the best offhand for you!
However, this is just theorycrafting. How about some real numbers?
Initial testing with a target dummy seems to confirm my tests. Additionally, last night to finish off 10man Naxx I threw mongoose on a
[Blade of Dormant Memories] to replace my normal
[Kel'Thuzad's Reach], to use along side my
[Pride]. There was a noticeable DPS increase. Especially on Loatheb where flametongue did nearly 40% of my total damage.
Now I could upload a WWS for you guys if you really want, however I'm not sure how much it would prove to you. I started the instance without maxed dagger weapon skill (about 370), and it didn't get maxed out until after all of Plague wing, and Anub/Grand Widow. Additionally, it was only Spider/Plague wings and KT, and as I don't have a good data set from a previous week to compare it to. Furthermore, I didn't use consumables, and for all you know I might do 5600dps on Loatheb and 3500dps on Grand Window with my 10man gear normally. So really, I urge other people who actually have better gear than I to actually try it yourself and post your data.
Now between losing the post, and having to delay posting this i've forgotten what else I had to say. So i'll just post it in a list as it comes to me:
-As Rounced said, next patch the Windfury Glyph is getting a make over. However, i'm not so sure it will make up for the dps gap. Remember, that if I were to respec, switch my Windfury Glyph to Lightning Shield, and regem/enchant the gap becomes much larger.
-Hit rating becomes more important with these weapons and setup with so much damage coming from flametongue. With Heroism I got my mainhand down to attacking at 0.86 speed. With my average crit on a Flametongue at 950, missing can add up fast and hit you pretty hard.
-Threat might become something you have to watch. When literally 80% of your damage is coming from magic sources, spirit weapons doesn't help that much.