I think that Hardcore mode should increase chances for Zombies And Skeletons wearing armor.
Chance for Mobs wearing armor: 65.0%
Chance for Mobs getting level 30 enchantments: 35.5%
When you reach maximum difficulty on Hardcore, there is a big chance for zombies wearing diamond armor. Diamond armor can get up to Level 20 enchantments. It should also increase the chances for spiders having potions.
Zombies should also spawn with iron pickaxes, and axes, diamond pickaxes, shovel, axes. Can also get up to level 30. (35.5%)