On the very rare occasion where the boss is about to die or you're anticipating an imminent string of crits, there are other ways of dealing with those situations than to interrupt a fireball (ie, don't cast the fireball in the first place and do something else).

Queuing spells is an extremely important part of maximum dps. By "queue" I mean casually spamming the next spell towards the end of the current cast or GCD. The next spell will cast the moment the server allows it to. Yes, you can queue instant cast spells such as HS Pyro and LB. Example: Fireball -> Hot Streak proc -> Fireball -> Pyro. Obviously you can't spam the stopcasting macro during the second fireball or you'll interrupt it, and if you're not queuing it then you're losing seconds of dps throughout the course of the fight.

Also, you can't "anticipate" hot streaks. Going through with your current spell is always important, and that's true for all specs. It's the same reason why arcane mages couldn't rely on missile barrage proccing on the third arcane blast before arcane barrage was nerfed. I'm not gonna do the math for your scenario but I would guess interrupting your fireball hoping to prevent munching future potential hot streaks is a losing proposition.

Just tested outside Ironforge, glyphed provides the normal pushback of damage but no interrupt.

I have a couple of questions, I went through the armory of the mages in ensidia, paragon, and premonition and I noticed a couple of things I can't figure out.

1. They all have ffb as their dual spec. I can't think of a time in heroic trial 25 where I would want to be ffb instead of fire.

2. A lot of them have combustion, which I didn't think was a very good talent.

Anyone have any clue?

Perhaps it is still there from Ulduar, where several encounters (Vezax, Hodir, etc) favored Frostfire. Yes, Fireball can work quite dandy through all of Trial of the (Grand) Crusader, so there isn't much need for your dual spec. Perhaps they still run Ulduar (for the head mount) or are just lazy.

Combustion is not a Great talent. However, it isn't completely worthless. It's one talent point. Perhaps that's where they felt it was best needed.

I'll risk replying here despite the forum rules regarding heroic Anub discussions because the following thoughts are true for FFB specs in general, and because the particularities may be applied to the non-heroic version of the encounter as well.

Now then. Why wouldn't a mage be willing to run a 0/2 Flame Throwing FFB spec? The talent does not affect your primary nuke, so unless you're responsible for scorching, I don't really see the point in spending any points there. Even then, the fight does not require any movement while the boss is surfaced, which is the most crucial phase for maximizing dps.

I've also seen mages spending the "floater" points in Permafrost. This is a more intelligent choice for the fight as it allows for better kiting of the Swarm Scarabs while the boss is submerged. Tanking them is not ideal, so ranged are normally responsible for generating the most threat.

However, I have found the Fiery Payback talent to be the most useful for this encounter, specifically for the final phase in which Leeching Swarm is active. While the cast reduction on pyroblast might not effect a new rotation (to be clear, I have not tested this), the damage reduction proves very helpful as your healers struggle to keep everyone just barely alive.

Just want to point out that regardless of how you go about casting Pyroblast (Hot Streak proc or just normal cast) when under 35% health you will incur the 5 second cooldown on Pyroblast if specced for Fiery Payback. The other benefits from the talent may well justify this potential loss in Pyroblast casts however.

I personally find this true when you're chaincasting spells with casting time, but I feel as though it's actually better to not spam the next spell's button while in a GCD as it seems to incur another GCD lock, hence causing there to be a 2s or so pause between the instant cast spell (with only GCD) and the next spell that's casted (e.g. Fireball). This is from practice, I've no idea if it's true, but I do recall from reading wowhead's comments some time ago on the Rapid Defense achievement and there was a post on the mechanics of that vehicle and I seem to find it similar between that and using instant pyros from HS triggering the GCD, hence if you try and use the next spell too quick it'll incur yet another one. I do play in high latency too, as suggested in the post(400-600ms) and experience the same kind of delay if I try mashing Fireball's button right after a Hot Streak's pyro.

I meant you could fit Combustion and 3/3 SotM into a Fireball spec if you went 0/2 Flamethrowing.

I used to do FS9 -> FS8 -> Blizz -> (repeat) but since 3.2 I've switched to this: LB -> tab LB -> tab LB -> tab LB (until everyone has LB) -> Blizz (until first LB explodes) -> (Repeat). Granted, LB requires 11s to explode, and then every 1.5s later, but if the fight will last longer than 20s (and none of the adds die before that time), it's better DPS to keep LBing if all of the 'first batch' will explode their LBs. If there's something like 4 adds I use Blizzard as filler between the 4th LB and the next wave of LBs after explosion.

Also, if there's one among the pack of adds being AoE'ed that's stronger/need to be killed earlier than the others, then target him for the Hot Streaks that you will get. Of course this one works when there's alot of adds that don't die that fast (In Uld25 mainly). Sometimes when there's more than 7 I just keep tabbing LB (phase 2 Black Knight, Freya adds, etc) - 17k dps on Freya trash don't lie :p Try it out.

OK I am just going to put this out there, there is no reason to be making a big deal out of which spec does better AoE.
In all cases Blizz does at least 8k dps no matter which spec, besides you will just be out-dps'd by a rogue and their fan of knives anyway.

The only real downside of arcane aoe is lack of threat reduction. Outside of that its somewhat very comparable to ffb.