On a one-minute single-boss fight the build is 11/35/5. It runs the Fire tree down to 
Combustion, takes five Frost points for 
Elemental Precision's hit, and puts the rest in Arcane.
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0/1230105-23552020130123051-005On one boss the Arcane points buy 
Arcane Concentration, whose Clearcasting makes about one landed spell in ten free.
Why these talents
Heating Up is new in Forever and drives the rotation. Each crit from 
Fireball, 
Fire Blast or 
Scorch takes 25 % off your next 
Pyroblast, up to three stacks, so three crits turn a six-second cast into 1.5 seconds. It needs the Pyroblast talent, and the two are worth the same, 9.4 %, because taking Pyroblast away removes Heating Up too.
Ignite burns the target for 40 % of every Fire crit over four seconds and is worth 13.5 %. In Forever each mage has its own Ignite, and a new crit adds what the running burn still owed instead of overwriting it. The burn copies the crit after all your bonuses and takes none again, so Fire Power and Fire Vulnerability count once.
Improved Scorch makes every Scorch add a stack of Fire Vulnerability: 3 % more Fire damage from you, up to five stacks, for 30 seconds. It is worth 18.5 %. On some fights its value tops the debuff's 15 %: without stacks, the Scorch line never stops firing and pushes out Fireball or Flamestrike.
Incineration adds 6 % crit to Fire Blast and Scorch, the two spells you cast most on long fights. It is worth 6.1 % on a three-minute single-boss fight, where Scorch is the filler, and 2.4 % on a two-minute single-boss fight, where Fireball is.
Fire Power and 
Critical Mass are the flat ones: 10 % Fire damage and 6 % Fire crit, worth 9.1 % and 5.3 %. A point of crit is worth more than the same point of damage would suggest, since each crit also starts an Ignite and a Heating Up stack.
Elemental Precision is now plain hit with Fire and Frost spells, 5 % at 5/5 in the talent data, and worth 5.9 %. Its tooltip still prints 6 %, but the simulator uses the 5 % the ranks give.
Combustion (8.3 %) and 
Master of Elements (0.0 %) complete the build. Combustion is a single use on fights up to three minutes, so it is worth most on short ones. Master of Elements returns 30 % of a crit spell's base mana. It grows with fight length on one boss and counts at every length on three, where each Flamestrike costs 990 mana.
Flexible points
A few points add nothing to a boss simulation. Some open the next row and the rest have nowhere better to go, so spend them on what your raid needs.
- Wand Specialization and Arcane Focus. Five points in Arcane's first row open its second, where Arcane Concentration sits. Wand Specialization is worth 0.0 % and Arcane Focus 0.0 %, since our simulator never fires a wand and Fire's only Arcane spell is Arcane Explosion on three bosses. Any five first-row points do the same job.
- Flame Throwing. The simulator stands 20 yards from the boss, inside Fire Blast's range of 20 yards, so the extra 6 yards show as 0.0 %. In a raid they let you Fire Blast from 26 yards.
- Burning Soul. It cuts your Fire threat, by 20 % at 2/3 and 30 % at 3/3, and protects casts from pushback. The simulated boss never hits you and threat isn't scored, so it reads as 0.0 %, but in a raid that is where spare Fire points belong.
- Arcane Subtlety. Some builds take a point. The simulated boss has no resistances, so it does nothing here. Forever's rules for spell piercing aren't in our simulator yet, so treat that zero as unmeasured.
- Improved Fireball. Five points for half a second off Fireball. On a three-minute single-boss fight you only cast Fireball before the pull, so they are worth 0.0 % there, against 8.4 % on a two-minute single-boss fight.
What each talent is worth
Each figure is the DPS the build drops when the talent is taken out and the fights are run again. They overlap, so don't add them up. When a point is spare, the last-point column is the one to compare.
On every fight
Each fight and faction is searched on its own. The one-boss builds only trade points of no value: Arcane Subtlety, a point of Burning Soul or of Master of Elements. The three-boss builds move real points. They take 
Improved Flamestrike 3/3 and 
Blast Wave, which is worth 2.9 % on a three-minute fight against three bosses. On two and three minutes they pay for them out of Improved Fireball and Wake of Fire, and Arcane Concentration is worth 14.1 % there, because a free Flamestrike saves 990 mana. On one minute the three-boss build skips Arcane Concentration and keeps Improved Fireball 5/5, Wake of Fire 2/2 and Flame Throwing instead.