Unless you are going to be doing some racing at the track then you will be happy with a 600. The liter bikes are for those who have had some serious seat time, so if that is not you and you do not have the will power to stay out of go grip I would stick to the 600's. Most 05 600's will run with a stock liter bike from 98-00 if you have the guts to run the bike up to the limit. I just purchased a new Kawi ZX-6R which is a 636cc motor that if FI. This bike will flat out move. So the big question is how much do you want to spend on a bike you know you will drop at least once. Answer that question and the rest come easy.