Expertise for MTing pallies - how much does it help?

Umm, was just reading the original post, and I wonder, did you really mean this as an OT ability? Barring specific fights (troll phase of Nalarak, Halazzi, Bloodboil, basically anything with a splitting cleave) why would the OT stand in front of the boss? Once behind him he has no block or parry anyway, so its effectiveness is reduced, isn't it more an MT ability where you need to stand in front of the boss (else he turns round to stand in front of you)?
_________________
Ahh, but you have heard of me.

http://eu.wowarmory.com/character-sheet.xml?r=Lightbringer&n=elyria

It makes sense that WF would eventually pass Wizard Oil, because WF scales whereas oil does not.

The question is how much spell damage do you need before that happens.

As for me, I'll be keeping my wizard oil for a while now, although we don't have enough shamans to put one in my group anyway.
_________________

Well, WF basically increase your white + SoR damage by 20%. If those are around 35% of your damage-based threat, that puts it at a 7% overall threat gain. Since 42 +dam ~= 21 tps, they' be equal at aroun 300 tps from damage. No surprise there, the claim has never been that Wizard oil alone is better than WF. The kicker was always that if not using WF allows you to use WF instead, it's a tradeoff not of 42 +dam vs WF, but of 143 dam vs WF.

From that with the assumptions above, the cutoff point is around 1050 tps from damage alone. Of course, at the gear level where that tps is attainable, I'm not sure that melee + SoR is still making 35% of your damage based tps....I haven't gotten a good reference WWS lately (and I'm not generating them myself, being retired from raiding).
_________________

hit isn't 100% but it ignores parry and block and dodge iirc, meaning its just the base miss chance which expertise doesn't affect anyway.

Stuff like Supremus can be OT'd from the back, not really sure about the parry gibbing, never seen it happen tbh, or if it has it was a welcome addition to the mana pool / rage pool.
_________________
Ahh, but you have heard of me.

http://eu.wowarmory.com/character-sheet.xml?r=Lightbringer&n=elyria

Bosses can dodge you if you are behind them. They cannot parry or block you though.

And parry gibbing is usually associated with Death. We only notice the parries that kill us, and we regularly miss the others.
_________________

I did some quick math on it a week or two ago, I worked out that for me personally WF was 55 TPS (my spell dmg has gone up since then and a lot of people around here in SWP have more spell dmg than me, so for you people its more, I think i did this calculation with 500 unbuffed SD).

Oil is 21-23 TPS;
WoA is 50.5-54 TPS;

(I use 1 spell dmg is between 0.5TPS and a little bit more than 0.5TPS as we block a load more in SWP on average)

However, if you use Oil you can't use WF, so Oil + WoA > WF.

Note that in WotLK, WF is a buff and WILL STACK WITH WEAPON BUFFS (confirmed by blizzard). In this case, WF > WoA (and ofc Oil + WF > Oil + WoA) for single target tanking. This is only with the current ranks of said totems and oils, at level 80 it will probably be a bit different but in the end it will probably be the same as it is now.
_________________