Wish said:
I'm a big fan of Empower through the mid levels. At 10th level, your Cone of Cold takes a 5th level slot and does 35 damage on average. Your Empowered Fireball takes a 5th level slot for 52 damage on average. Pretty nice.
But, you must also remember that the DC is 2 better for the Cone of Cold.
18 stat caster, spell DC 19 versus spell DC 17
Low Reflex 10th level opponent (+5 for example)
45% chance 26 points + 55% chance 52 points
versus
35% chance 17 points + 65% chance 35 points
Empowered Fireball averages: 40
Cone of Cold averages: 29
Not quite the 50% increase that it first appeared (in this case), closer to 40%. Still good though, but 10th level is the optimal level for this (or again at 15th level for Empowered Cone of Cold versus Delayed Blast Fireball).
And against a 10th level Rogue with a Reflex save of +11, it becomes:
Empowered Fireball averages: 13 (6 with Improved Evasion)
Cone of Cold averages: 12 (6 with Improved Evasion)
Not significantly better at all against this type of opponent. It all depends on the situation.