@fubar_prime At the end of the series you could always level yourself up and give yourself end game weapons and armor, then fast forward to like day 210 or something and see what the end game hordes are like.
@ApoEngineering Snufkin's Zombies Plus and Guppy's Zombies are two mods that add harder zombies to vanilla. Also try the Hidden Lights 10k Map. The map is huge but there are lots of custom POIs.