You've got a Baltimore Class CA already in the game, you aren't going to get a much better design than that if you intend to improve the cruiser, unless you move into the Alaska-Class CB, which were white elephants by the time they were launched anyway.
Light cruisers - 4, 5, or 6" guns
Heavy cruisers, 6" 8"
Battlecruisers, pocket battleship - 11" (German Graf Spee), 12" guns (Alaska Class)
Battleships - 14, 15, 16, or 18" guns
So if you intend to upgrade the cruiser, you can go with one of the Alaska-class CBs, or perhaps a German pocket battleship.
Your next step from there is one of the pre-war BBs, Pennsy, Nevada, California, etc.
Next step from there is a Treaty BB like KGV class, SoDak, etc.
From there, Iowa, Yamato