600cc starter bike or smaller?

I am 23 and just getting into sport bikes... I have been looking around and talking to people about a good starter bike while looking at gear. I have had about 50-50 results regarding where I should start. I'm a big guy and I have people tell me I might as well go ahead and get something 600cc if that's eventually where I'm going to go (which it is)... whereas others have told me I should start with the 492cc Buell Blast or something similar since that's what they use in the MSF course in town (which I will definitely be taking). The people who have said just go with a 600cc used CBR or something similar because after about a month on the Blast I'll wanna get something bigger real quick... keep in mind I have never ridden a motorcycle in my life :-P What do you suggest? Thanks!

First, take a course to learn to ride... That was my first step. Then I rode a relative's 500 for a summer. This year, I decided to buy my own bike, an 800. But to start with, power/size isn't really an issue. It's learing to ride! I'd say a 600 would be okay. But if you found a 500 to be more affordable, I wouldn't hesitate to pick it up. You won't lose a ton of money if you buy it used and take care of it for a year or two. And you also won't be out lots of money in case you do make a mistake and dump it.