Depends on a number of factors – type of chassis, type of wheels, type of tires, and more importantly, who is driving.
At a track like Rock Island, with all drivers on 5″ wheels: CIK chassis, 4-Cycle chassis, laydown seat, CIK seat, big nose, CIK nose, they all ran together at the front. It really comes down to who’s driving.
If the class is just getting started, keep things open to bring in as many people as you can. Keeping tire costs to a minimum is another good thing, so not to force racers to buy a new set every club race.