If you are just riding on the street a 600 is fine to start but you will probably want to upgrade quickly. If you go to the track stick with a 600, you'll get better faster. I can't tell you how many times I see people on 750's and 1000's get spanked by under 500cc bikes that aren't even sport bikes. I've got an 04 SV650s with GSXR suspension/brakes and its a perfect compromise for me between track and DD use since it is my DD when its not raining. My next bike will either be an SV1000 or a Ducati 848, depending on which route I chose to go.