Prior to reading this thread I did a small study, just out of curiosity, to see what the difference was between class levels. I did not look at each class level in its entirety because that would have required far more time than I wanted to devote to the matter. So I just looked at the Freeman ratings for the most successful program in each class over the last five years. The Freeman ratings are the base computer ratings used by CalPreps.
The result was that, on average, there is a 4 point difference between each class level (3.93 points to be exact). That translates to roughly a one game difference per level. So a 9-0 3A team would be equivalent to an 8-1 4A team. It should not be surprising, though, that the difference is not uniform from level to level. And the differences change over time. Ten to fifteen years ago there was little difference between 7A and 8A. Now, with Lincoln-Way East having absorbed more students and the great Wheaton-Warrenville South teams having faded into the past, the difference between 8A and 7A is the largest of the class differences (12 points). 7A is now much, much closer to 6A. This explains why Huntley can be competitive with Cary-Grove and Prairie Ridge, but they tend to do very little in the 8A playoffs. Similarly, Glenbard West was consistently a championship contender in 7A, but has not made it to a championship game over the last five years in 8A.
While there is a 12-point difference between 8A and 7A, the total difference from 7A down to 4A is only 9-1/2 points. This explains why Rochester moved successfully from 4A up to 5A and Nazareth moved successfully from 5A up to 7A. There is roughly a 10-point gap from 4A down to both 3A and 1A. This seemingly strange result is due to the fact that 1A is very top heavy, with both Lena-Winslow and Forreston being powerful 1A programs. There is a large drop in 1A after those two programs. The 2A class level, at least at the top, is the weakest of the eight classes. It is 10-1/2 points worse than 3A.
The methodology used in this abbreviated study would not pass scientific scrutiny, but it does give some indication of the differences between classes. While 8A is clearly the powerhouse, the surprising conclusion is that there is not a huge difference between 4A, 5A, 6A and 7A.