Don't forget that bane does 0 damage on the first target, as that's what you're spreading from, while painflare does do damage to that.
A table that compares them (max duration is simply 10 times of the 1-tick version):
Code:
Targets Painflare Bane (1 tick) Bane (5 ticks)
1       200       0             0
2       400       80            400
3       600       144           720
4       800       192           960
5       1000      224           1120
6       1200      240           1200
7       1400      256           1280
If you think the fight will last 15s or longer, use bane, if you think it's shorter, use bane anyway, but just to get in DWT after 5s.