Par score requirement: 14,000.
I got this first try using this method:
Although I did have practice speed-running for
Difficulty: Legendary.(Recommended actually is Heroic--more people had success that way--if you use Heroic, make sure to get more kills than I detail in this solution to make up for loss of points)
Skulls: Catch, Famine, Thunderstorm, and Tough Luck.
There's several important steps, fortunately the main point gathering is at the beginning of the mission so you can die later without worrying about resetting your points streak!
1. Run for one of the Warthogs that comes from the right side with a gunner already in it. You're going to use this Warthog to kill everything in the first area. Drive around at high speeds trying to get behind Choppers and Ghosts so your gunner can eliminate them, and AVOID getting close to the Wraith or it will tear you up with the Plasma gunner on it. Continue circling this area until all enemies are gone, and DO NOT stop moving for an instant. Once you've destroyed about 4 Ghosts(there will be a drop ship coming in dropping a Ghost), 2 Wraiths, 3 Choppers, and a variety of ground units, you're ready for the next part.Point gathering should be done! I had about 23,000 points here.(Note: an optional approach is not spending as much time at step 1, and instead using the Spartan Laser at the large building in step 5 and take out the Wraith's for a LOT of points)
2. Switch out your Warthog for one of the other Marine Warthogs which should be just hanging back near the start(that's where my 2nd one was) if you haven't already switched.
3. Drive through the mission, past the 2nd Wraith, and change your Warthog for the Ghost that's parked on the little hill facing the way you come.
4. Keep driving until you see the long hillside with 3 turrets along the top facing you. Using the Ghost, boost up the steep cliff a little to the right of the last turret to the right. If done right, you should be able to just boost up the cliff--aim to the right so you end up far to the right when you get over the cliff to avoid getting shot, and boost around the next corners.
5. In this wide open area, there's a health pack right in front of the railing on the right. Then jump the railing behind the benches and head almost exactly straight for the door you need to go through. You'll climb up the first rocks, and if you hit them right you should be up and over easily. The bumping over everything makes it hard for the Covenant to hit you with the turrets, and you just need to keep going as fast as you can while avoiding running into anything. Drop over the far cliff, and floor it for the doorway. Dodge around the corner as soon as you get inside to avoid getting hit too much from behind. (Optional approach to this area, head to the large building, and grab the Spartan Laser that is in it.. take out the Wraiths, then waltz out of there)
6. Cross the bridge, swap out for the Ghost on the other side, and grab the health pack on the left wall just before leaving the building at the end of the bridge.
7. Continue boosting... when you go around a sharp blind corner to the right, start climbing the cliff on the left side, and about 2-300 feet past the corner you should be able to boost up and over the cliff edge. Take a left on top of the cliff, and get ready to make 2 very sharp right turns to get past the Ghost and Wraith.
8. For the last part here, roadkill some Brutes for fun(and points!) if you can, then boost through the middle once you see Covenant on both sides. Try to go just to the right side of the rock that's in the middle, you should be able to boost through the center of the area and up the 8 foot cliff on the other side. Boost to the right for about 5 seconds and you're done!
I finished with ~24,600 points in 7:37 time.