I'd respectfully suggest that it's not possible to "prove" that the 7" wheels don't provide an advantage over 6" wheels. And even if repeatable tests demonstrated that it was the case, the results won't generalize to accommodate all of the other potential variables (e.g., fender width, cars with relatively high race weights).

I'll ignore the question of PERCEPTIONS of competitive advantage. That's another ball of worms.

There just aren't any "good" answers. They all seem "obvious" but only if viewed from one perspective or another. The clearest answer I've heard on the subject is that allowing 7" wheels is a money-saving answer if and only if that's all you've got. Otherwise it's a money spender.

K