I don't know. I fought using my spear and have killed all levels if zombies easily. Only bears and dire wolves are any actually challenge. Sure, you might need an extra hit or two with a weapon that is appropriate for what you are fighting and that you are perked into, not that isn't really bad. I wouldn't even consider the radiated to be bullet sponges. I can kill them in only a few headshots with my spear.
If anything feels a bit more tanky, it is the mutated zombie. That one seems to take more hits than normal.
