Try having the game set to ultra, but having the game stiff you and give you no water reflections, despite ultra being what the game auto set itself to based on your hardware..

The shooter of shooters, if there is a game that can slow halo, it's Half-Life. I remember when Half-life 2 was in development, the debates and arguments of which was better, Halo 2 or Half-life 2 (most of the time Half-life 2 got the win, though not always). Now's a perfect time to relive this classic, as a true remake is coming this year, Black Mesa, google that :P

There is a difference in shadows, the lower the quality, the sharper and blockier, I know, I run at low shadows for framerate.