While a 600 is a good race bike, I guess I am old-school and feel that a lightweight bike is
still the best way to go. It used to be a good EX500 or FZR400 was the ticket, but the SV650 is now the bike to get.
There are all sorts of reasons a LW bike makes sense as a first race bike, and a few reasons you shouldn't - and if you want specifics, feel free to ask. In a nutshell, SVs handle great, easy to race prep for cheap(er), are easier on tires, the classes are fun, and the power will not get you into trouble.
Oh, there is nothing more fun in this world than passing a 110HP 600 supersport machine on a 68HP "ladies sport tourer" on the outside in turn 1 when you come to terms with the machine.
(oh, I will just add that I have raced everything from RS125s and TZ250s to Ducati superbikes and R1s - and decided race an SV650 this season in addition to my 600 just because they are so much fun)