SettingsShadow and fidelity settings affect performance and the look of the game tremendously. Shadows take up a huge amount of processing power since the video card has to track the silhouettes of 300 units simultaneously. Fidelity is probably the most important game setting you can use to balance out performance and graphics. Low fidelity settings will give you enormous performance gains, but the game won't be very pretty.
The level of detail setting changes when the game decides to load in more complex graphics depending upon your zoom level. With a high level of detail you can zoom out pretty far and still see your units. However, with a low level of detail, the game turns your units into little icons at closer zoom levels, which reduces the graphical load a decent amount.
(Longer bars indicate better performance)
Quality Settings, 1600x1200
Background Image, 1600x1200
Shadow Fidelity, 1600x1200
Texture Detail, 1600x1200
Level of Detail, 1600x1200
System Setup: Intel Core 2 X6800, Intel 975XBX2, 2GB Corsair XMS Memory (1GB x 2), 160GB Seagate 7200.7 SATA Hard Disk Drive, Windows XP Professional SP2. Graphics Cards: Radeon X1950 XTX, Catalyst 7.1.