Looking at the MARRS results, where both classes are well represented, both have similar levels of competitiveness. The top tier cars are pretty close, the middle isn't too far back, and the last third is all over the place.

With a Spec RX-7, the timing, carb, and plug adjustments are pretty well known - at least in the DC region - where several of the tinkerers in the group published their tuning tricks for all to see.