Simple tweaks that can greatly increase your perf without much image Q loss .
Specular : you can get as much as 40% performance increase with this OFF , you won't miss the shiny metal when you see how fast the game moves
Shadows : who cares if you can see shadows? big perf gain here
Shaders : Optimise the game for your graphics card by doing the following :
Go into halo shorcut and add -usexx to the end of the file's location . Find out what vcard you have and optimise the shaders for the following :
Geforce FX 5200-5800 : set shaders to "use14" or "use11" for increased performance . This decreases the quaility of water effects [ if you have a pixel shader card] and the detail of bump mapping/mip mapping .
Radeon 8500-9200 : set shaders to "use14" , radeon cards are proven to be nearly 2x faster for halo .
Geforce 3-4 : set shaders to "use11" for geforce 3 and "use14" for geforce 4's , if performance is not enough for the 4s decrease it to "use11"
Get CAT 3.9 and Forceware , big perf increases in these two and halo doesn't crash anymore with 3.9