Try these settings:

VSync : Disabled

TEXTURES
Video Memory : 2048 MB (Acctually my card only haves 1024 MB, Dunno why I set it to 2048 MB. But I'm just gonna leave it there, maybe it also increases some performence)
Texture Detail : Normal
Texture Filtering : High

QUALITY
Objects : Very low
Terrain : Normal
Clouds : Low
Shadows : Disabled! (Try disabling this!)

Rendering
Antiaiasing : Low
Alpha to Coverage : Disabled
Edge Smoothing : Disabled
HDR Quality : Very Low
Ambient Occlusion : Disabled
Postprocess Quality : Disabled
Bloom & Rotation Blur are off

More information here