SUPER END GAME SPOILER WARNING but you should read because its a easy boost/fast method.
*** Spoiler - click to reveal ***On the last mission when you are fighting Zinyak and he turns into a robot, there is a part where you have to throw CIDS at him. Throw some at him until he starts spawning aliens. Dont throw anymore CIDS at him and just use the super stomp power on the CIDS and aliens until you get the 1000 kills. SUPER easy may take 30 mins. You can then use the other super powers to get the other kill achievements.