5A is West Point, Ridgeland, Pearl, etc.
I would argue that St. Stanislaus vs. West Point (4A vs. 5A champs last year) would have been an epic game, and either could have beaten any 6A team in the state sans South Panola.
4A is probably more competitive top to bottom (Louisville, Noxubee County), but their is more parity in 5A. There were 6 schools that could have come out of the South 5A bracket last year, for instance.