This was the only level i didn't manage to pick up after my legendary and co op legendary runs so i wanted to share how i got this.
Ok so i set it to legendary and then put on Famine and Thunderstorm. As you will be in Banshees and picking up weapons from crates (which aren't affected by famine) and Thunderstorm on Halo 3 and ODST doesn't really do much - definitely put these on.
Now you will also want to put on Tilt (or alternatively tough luck). I think i chose Tilt as personally i hate tough luck as it makes overcharge PPing brutes a nightmare. I also didn't go with catch as i found the first area horrible! I would recommend Tilt though.
Now the absolute key to getting the points on this mission is.... Destroy all the spare banshees after you leave a section. I think i was getting at least 800 points for each one.
Tips wise for the only room you have to fight on foot in if you go straight across from the door then there is a box of snipers and carbines at the base of the stairs. Also make sure you find and overcharge PP the engineer.
In the end on this mission i was well over double the time but i finished with about 55,000 points or so. Hope this helps someone. With this setup it was pretty easy to get the score in my first attempt.