First time I stepped into a heroic was at 603 (used gear in bags). Skyreach, having never ran it, i spent more time worrying about avoiding shit than doing dps. It was also the first time I played destro. I was a pretty shitty dps (like 5k? Dunno I got kicked and my meter reset, although I can't blame them).
Did MC at 605, managed to do about 10k-11k as destro (got much better at doing my rotation). Still kind of shitty geared (ala low crit/high haste from being affliction). I too hope they do a little balancing pass. From what I understand though, any spec relying on crit sucks balls atm (fire mage, destro lock, fury war).