I have a FO/Hydra sorc.. 20 points in Hydra/FB/FM. I reach ~1.5k damage.
Hydra is fun (very cool, too) and all, but I end up using FO and fireball when I'm mf'ing, since they're faster.
Hydra is a pain in the a**. You spend 10 seconds setting them up, and even when you have 4 of them, you have to babysit and keep on casting them.
OT: I wish Blizzard will 'fix' Hydra.. like remove the cast timer, and instead just limit it to 4/5 Hydras. That way, you get maximum firepower in an instant without being OP.