It may depend on whether you are talking about all high schools in a given class (approximately 64 teams), or the entire playoff field in a given class (32 teams), or the top teams in a given class (semifinalists = 4 teams). You mention "from watching the state title games", so I suppose you are talking about the top teams. For what it is worth, here is the average CalPreps power rating for the four semifinalists in each class for 2023.
8A = 50.1
7A = 45.6 (4.5 points behind 8A)
6A = 35.0 (10.6 points behind 7A)
5A = 37.3 (2.3 points ahead of 6A)
4A = 27.3 (10.0 points behind 5A)
3A = 24.4 (2.9 points behind 4A)
2A = 16.2 (8.2 points behind 3A)
1A = 23.5 (7.3 points ahead of 2A)
That would seem to narrow things to three possibilities: The jump from 6A to 7A, the jump from 4A to 5A, or the jump from 2A to 3A.
Here is a list of the 13 regular season games played this past year between semifinal teams from different classes.
8A Loyola defeated 7A Mt. Carmel 23-21
8A Lincoln-Way East defeated 7A Batavia 14-13
8A York defeated 7A Downers Grove North 32-21
8A York defeated 5A Nazareth 42-13
7A Mt. Carmel defeated 6A East St. Louis 36-33
7A Mt. Carmel defeated 5A Providence 43-9
7A Downers Grove North defeated 5A St. Francis 27-22
5A Nazareth lost to 3A Montini 24-23
5A St. Francis defeated 4A St. Laurence 42-28
5A Providence defeated 3A Montini 38-7
5A Providence lost to 4A St. Laurence 31-24
4A St. Laurence lost to 3A Montini 24-17
4A Wheaton Academy lost to 1A Hope Academy 30-29
Given how closely East St. Louis played Mt. Carmel, I will eliminate the 6A to 7A jump from consideration. Given that 5A Providence lost to 4A St. Laurence, 5A Nazareth lost to 3A Montini, and we saw Rochester successfully make the jump to 5A in 2019, I will eliminate the 4A to 5A jump from consideration. Therefore, in my humble opinion, I will say the largest jump in team ability is from 2A to 3A. I think both Byron and Montini would have handled Wilmington fairly easily this past season (by 14 or more points). In fact, Wilmington has struggled a bit in the past when they have had to play in the 3A bracket.