[3.5]Greater Produce Flame (PEACH)

[Felyndiira]

So, assuming no metamagic reducers, you can use a single level 4 slot (or an extend rod) to double the damage of the cone of fire (20d6 + 10 at level 10), or use a single level 9 slot to do 1440d6 + X damage in a 30' wide cone, reflex save for half.

The spell definitely sounds interesting, although the cone of fire needs a cap. 20d4 for a fourth-level slot (or a third-level slot with an extend rod) is a bit on the good side, but ninth-level or not (less if you have an incantrix in your party), 1440d6...=p.