......However, the actual difference in damage is small. Let's run the numbers with a Ftr 6 with a Greatsword. He has Specialization, and a 18 Str. Criticals are included.
Our fighter has a choice: Buy a +2 sword, or a +1 Flaming sword. He decides to defer to the party's Wizard(algebraist)

to determine which is better. The wizard looks at 2 cases: where the Ftr hits half the time, and where the Ftr hits 3/4 of the time. Here's the expected damage per swing from each sword for each senario:
Code:
50% Hit 75% Hit
Greatsword +2: 10.3 15.0
Greatsword +1, Flaming: 10.6 15.8
So the flaming sword is better, yes?
How does it compare to a +3 sword?
Code:
50% Hit 75% Hit
Greatsword +3: 11.9 16.8
Greatsword +1, Flaming: 10.6 15.8
Check it out: a +3 sword is much better than +1,flaming. In fact, the difference between +1, flaming and +3 is much greater than between +2 and +1, flaming.
I'd say the energy bonus of +1d6 is very close to a +1 power.