Not apples v apples, but the 2 vs 4 seats dividing line is what separates two classes in one category in SCCA Solo, SM (Street Mod-4) vs SSM (Super Street Mod-2). There they allow more open engine swaps, still along manufacturer lines but with some sort of sliding weight scale or something for displacement and valves/cyl.

And although not apples/apples, this distinction actually holds more sway in road racing vs autocross because, as Kirk says, frontal area and overall aero comes more into play at the higher speeds.

So agreed. And precedent.

Will