Fastest I have gotten through an Endure was 1 hr, 42 mins. The main difference is I hang out to the right side of the first stair well and pick off grunts and jackels quickly with headshots. Chieftains quickly handeled with 1 charged plasma pistol 1 rocket. I could probably cutdown on the time by getting the bonus round points and dying immediately but I'm not one for dying, which is why I am proud of my 2 no death endure completions.