Battle of Ghen Crag is probably the better choice for this one. While it is not needed to get this achievement, it would be helpful to turn on the 'Time Press' modifier to help motivate you to go as fast as possible. Be aggressive but make sure to stay smart and try to flank around cover. Using the Reclaimer and Oppressor is a good combo, long range and high damage with the Reclaimer + basic gunfighting with the Oppressor. Just be quick moving from stage to stage and changing direction as enemies come from each corner.