2.2 Avg CMC, if Banefire is played for 3R on average and Wizard's Lightning is reliably R.  The "How Many Lands" guide says that should be 23-24 mana.  Goldfish some, and see what happens with 20 mana.

Counter-argument: I only have 5 cards in my deck that require more than 2 mana to cast.

"Jump-Start" Izzet mechanic lets you cast instants/sorceries from the graveyard, then exile the card.  Doesn't synergize at all with Enigma Drake. Good with Guttersnipe, though, because spells get cast twice.