With the changes to Torment the Weak and Pyromaniac, it is worth noting that a Fireball build does have the Magic Absorption advantage over Frostfire while maintaining DPS. There are, essentially, 2 floating points, starting from
18.51.0, to move around.
2/2 Magic Absorption, 1/2 Flame Throwing
2/2 Magic Absorption, 2/2 Flame Throwing, 4/5 Clearcasting
2/2 Magic Absorption, 2/2 Flame Throwing, 5/5 Clearcasting, 2/3 World in Flames
2/2 Magic Absorption, 0/2 Flame Throwing, 4/5 Clearcasting, 3/3 World in Flames, 2/2 Fiery Payback
Those are the four options I see as being viable. World in Flames does have added utility in DPS due to Living Bomb triggering Hot Streak in 3.0.8, so I can't justify dropping points from it. It works out to being a 0.5% DPS increase per point in 3.0.8. Magic Absorption is our base talent here, so it's always going to be 2/2. And if we're picking up Magic Absorption, then there is almost justification for picking up Fiery Payback as well. The goal is to increase survivability without sacrificing DPS (and one could argue to simply spec deep frost, but ice barrier is mana intensive and is a killer on the GCD if you're using it every CD).
While it's possible to pick up Fiery Payback quite easily with Frostfire (by simply removing points from Frost Channeling), the same can't be said about a Fireball build. There's no reason to raid without Burning Soul, and aside from that, Flame Throwing is the only talent that can be sacrificed and still pick up Fiery Payback. (Even though Playing with Fire increases spell damage taken, there's no reason to not take it still.)
My decision would be to first drop Flame Throwing, and then drop World in Flames. Clearcasting is tricky. While I don't have mana problems in the slightest with Frostifre in 25-man setting, I've never raided with Fireball. The added mana cost to Fireball, and the loss of Frost Channeling, may not be great enough to offset Clearcasting. However, with increased crit rate (3% from Focus Magic, 3% from Fireball Glyph), and 30% in-combat regen from Pyromaniac (in 3.0.8), mana may still be less of a concern.
Thus, I would certainly drop Flame Throwing, and then Clearcasting for Fiery Payback. On a fight like Sapphiron, when I typically have around 22,000 health, Fiery Payback would trigger at 7700 health. Without Fiery Payback, 7700 damage would kill me. With Fiery Payback, damage would be reduced to 6160. This means I would need to take 9625 damage with Fiery Payback to die. It's very trivial, but then, small increments is what a lot of things are about.