Solo round 30, 1 drone finished the round in 2 minutes.
Solo round 40, 2 drones finished the round in 5 minutes.
Depends on the spawn speed, as you go higher in rounds the spawn speed increases and therefore drone kills more.
2P round 30, 1 drone finished the round in 4 minutes.
2P round 4o, 2 drones finished the round in 5to10 minutes.
To accomplish this one player must remain in the center of the crazy place room running circles while other player must also stay in the crazy place and run around the outside wall losing zombies to the player in the middle who also has the drone, the drone must stay in the center of the room to take advantage of instant spawns. This strategy also works with more players but obviously will take longer.