The best replacement for overkill is exodus.

The best alternatives to overkill are rated as following:
★★★★★  exodus
★★★★  avenged sevenfold
★★★★  anthrax
★★★  kreator
★★★  megadeth
★★  ace of spades
★  umbrella chronicles
★  ensolite
★  warhead
  overkill
  testament

Your alternative for overkill is not listed? Suggest!
Speaking about overkill, one probably shouldn't forget about extermination.

Other search terms related to overkill and their ratings are:
★★★★★ extermination
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overkill
exodus
avenged sevenfold