5000 KillsG 50

THIS IS MY SOLUTION FOR THIS ACHIEVEMENT:

Team battle, point snatcher,
Lost Arena, short range (spawn kill)
Split battle on/off (on only doubles your kills, but halves your games played)
Kill limit is up to you, but you can do about 40 kills in 10 min. with only one person doing the killing.
This will also help you work on games played.

To keep randoms out just set the time limit for your match to 60 min. Most people won't want to play this for that long and leave, but you'll be done way faster than that.

Of course the more people you have won't get you any more kills but will make the time go a little fast. It also seems that teams are based on Rank the higher ranked individuals will be put against each other, it doesn't matter the order you join at all.