Indeed, Flak 16 has FC 8 and RF 6. Flak 36 has FC 10 and RF 8. There's also a version available of the 36 which has 35 AP rounds and 35 HE rounds. It's availability ends in dec '40. Cost is 94 at exp 70.
That makes the decision more difficult. I think I shade back towards the 36 then, as it will be needed to bring down at least 3-4 T34's or KV's per battle.