I would hit rock bottom and test it from there. ie: excellent with some landscape settings on medium.
Use IL2Setup and on the video tab set the following:
Settings: Custom
Texture Mipmap Filter: Bilinear
Texture Compression: None
Use Dither: On
Use Vertex Arrays: On
Polygon Stipple: On
Disable All: Off
Do an FPS test with Black Death and see what you get.