If you plan on any track time the hpi would not be a good choice. If you must go with an RTR here is a link to the few decent truggies i have seen at the track. It is going to be hard with a 600 budget.
http://www.amainhobbies.com/index.ph...y-Ready-to-Run
Have you looked at 1/8 buggy? In your price range you would have a better chance of getting something better. Also it is a little cheaper to race buggy cause parts don't wear as fast, tires are cheaper and last longer, etc.