Guys,
I have met and watched Cody Race. He seems to be a pretty level headed kid for his age and he can drag race a bike pretty danged good. He will be one that has to be delt with in PMRA. He has a pretty good support network of peers at the track in Eric and Aaron as well. I think Cody is looking for ways to make the purchase happen more than if he should start with a 1000+cc bike or not. Someone can act just as stupid on a 600 as a large bike. He has pretty much proven to me he has the skills to handle a larger bike.
Cody, the biggest problem you are going to have is the resistance to go fast on the street. Peer pressure is very hard to overcome even at my age. It is usually much more difficult at younger ages. Like said before insurance is going to be rough for your age and most places are going to require it to secure the loan. If it was drag only, you still have to worry about theft etc.
Not knowing much about whether you are in school still, living at home, working full time etc. You may be better off finding a bike that you can afford to buy out of your pocket. Maybe you can get your dad to sponsor you by paying some of your entry fees etc. Between payments, interest, and insurance you'll be paying much more than I think you realize.
Shoot you can race an older 9, 1000, or Busa (like you have been or about anything for that matter). Dad might even be more willing to help cosign for $1500-2000 instead of $4000 .