[blue00gt]

Like the others said, I wouldn't start on a 600. It sounds like a small, underpowered machine when you see all the 750s and liter-class bikes out there, but any newer 600 will kill you in a hurry too. I rode a VTR250 Interceptor for 2 years before buying a '90 Yamaha FZR600 and I still almost got into trouble on my 600 because it was (relative to the 250) so fast. I pulled power-wheelies without meaning to, spun the rear tire exiting corners and put my back out keeping from high-siding it, you name it. That 600 came with a little over 60hp stock and I modded it to over 80hp. The F3 and F4 you are talking about have more stock hp than my modded FZR did. We're talking low-11s bone stock with a decent rider.
So unless you have incredible self control, you would be riding with a serious handicap for a while on a 600. On a bike, more horsepower requires a lot more skill.