IMHO, a newer GSX-R600 is pretty damn fast if you're new to motorcycles. I cut my teeth years ago on a 440cc Kawasaki, and it scared the hell out of me the first few times I rode it. (And I'm 6'3, 300lbs... and it was REALLY slow.)
The GSXR is a great bike handling wise too; it inspires those confident feelings about your riding skills. Don't let it fool you. Even though I think just about any newer 600 is a bit too fast for a beginner, the high maneuverability of these bikes can make them pretty dangerous too. They're pretty easy to highside during an emergency swerve.
That all being said, if you ride it with respect until you become skilled enough to handle the situations that riding may throw at you; you should be just fine. And don't let me scare you; I know some guys that started out on ZX-11s way back when... and they all lived to tell about it.