In theory that means we can now macro Combustion and Impact. What's unclear is whether the Combustion dot will have 'landed' by the time Impact gets processed server-side.

That's not how the AoE cap works. If Blizzard damage has been increased by enough (and the mobs are stationary) then most likely it will be a case of Blastwave / Flamestrike for the DoT and Blizzard spam. We just need one of our theroycrafters to assess the numbers but on the face of it a 70% buff to its damage seems huge.

According to an earlier post in this thread, impact will spread any ignite created by the fire blast itself. I'd be shocked then if it didn't also spread combustion created immediately before that.

This change will be primarily useful when trying to spread a combustion off a relatively low health mob (so mostly trash and a subset of boss add waves). The risk of having a mob die from someone else's big crit between the combustion and impact will be eliminated. This, along with the ignite changes should help minimize the really bad encounter performances that fire mages sometime have.

In regards to watching for a good ignite in combustion helper, I wouldn't recommend it. The ignite needs to tick and we all know in that short window of time, from application to tick, we could lose our huge ignite to some dot tick. the way I deal with this is I ALSO run mage nuggets ignite watcher. It seems to stream live your current ignite on the target. sine it dosen't have to wait for a tick you can land a huge combustion before the ignite even ticks. Just what I do.

I am also very interested in this combustion+impact macro. That would help a lot.

Another possibility for this combustion change is to macro it with living bomb. Even with the invisible travel time this will ensure you always have LB ticking when combustion lands, and is one less thing to keep track of during those critical moments when you're hunting for a large ignite stack.

A solid mage should always have LB on their target, but every now and then I will have it fall off just as I cast combustion because I was focusing so much on my spell crits and ignite refreshes.

I don't see how a dot would eat your ignite, there is no munching with ignite ticks as far as I know. And for live damage of ignite this is coming with next version of CombustionHelper. Though as for Mage nuggets, live ignite report won't be as accurate as reporting actual damage from combat log, again because of munching.

When Cauterize is used to circumvent casting impediments, as described, is there really a resulting DPS benefit, or just an overall damage-dealt benefit? I can't see how it improves your damage rate during its proc. Am I missing something?

I don't think Blizzard is going to be a viable way to AoE as fire. Even as frost the spell is really bad on live realms at the moment. Should Blizzard turn out to be viable as fire or arcane, I doubt that is the intend, and will most likely get fixed. As I see it, the changes to Blizzard and AE is intended to make arcanespec and frostspec able to do AoE damage compareable to other dps specs - currently both are really lacking behind in this role. This would also be in line with the different ways to AoE pr spec the warlocks have.

Fot those discussing of AOE rotation, please note that the regular Flamestrike dot stack with the Flamestrike dot procced by Improved Flamestrike (of course if your Blastwave hit 2 or more targets).

CombustionHelper will be tracking these two in the next version.

This isn't quite true. On the heroic halfus encounter, the adds are relatively stationary in a small enough area for blizzard to hit every target at once. This assumes that the adds are stacked properly and interrupts take place appropriately. However, I think the AoE damage cap may reduce the attractiveness of blizzard in that fight because, as I understand it, blizzard would be affected by the target amount cap while ignites and combustions spread via ignite would not be affected.

I've been looking into Combustion lately and I just can't figure out how it works so if anyone has any insight I'd like to hear it. The tests were performed with fire spec, no glyphs, no fire power, one point in critical mass and no debuffs. In each case I just combusted a living bomb with no procs.

1) 197 spell power, 22.4% flashburn

living bomb tick: 715
combustion tick: 288

2) 4884 spell power, 44.268% flashburn

living bomb tick: 2875
combustion tick: 1273

3) 5199 spell power, 44.268% flashburn

living bomb tick: 3012
combustion tick: 1332

In each case living bomb tick matches exactly the predicted theoretical value of (403 + 0.233 * spell power) * 1.25 * (1 + flashburn + 0.05).

Now from all I know combustion should have dealt one third of living bomb tick value since living bomb ticks once every 3 seconds. From some other tests I confirmed that combustion tick scales the same way with fire power and critical mass as the living bomb tick. So the only thing that I can't figure out is the base conversion. I can't explain it with flashburn or any other multiplier. It almost seems as it's using completely different base and spell coefficient for the purposes of computing combustion. The only problem is that when I tried to fit the coefficients I wasn't able to get anything consistent with data so far.