I think 2 classes is enough for class seperation. ( sportsman and pro)
here is an idea.
Anyone who is sponsored by any MANUFACTURER should run pro.
Anyone who is sponsored by a LOCAL HOBBY SHOP can run sportsman or pro.
After that it is up to the race director to monitor the times in sportsman to keep it fair. One thing to remenber is your only talking about a few who would be sandbagging. It would be easy for the race director to police and bump the guys to pro. And sportsman classes should NEVER have a sponsorship form to fill out for the A.
running a sportsman, expert, and pro class would make it difficult on the race director as far as awards and the time it would take to run the mains. your talking cash payout for pro and double the amount of product for the other 2. not to mention more trophies.