Using a Radeon 9800 Pro, below is my video8.cfg file.
104712,VideoVersion
1600,Width
1200,Height
32,ColorDebth
1,DeviceCnt
DVRADEON 9800 PRO
0,MaxFPS
1,MipMapEnabled
0,DisablePalettizedTextures
0,PixelShaders
0,VertexShaders
0,MaxTexSize
31,OptionFlags
0.2,LOD
0.2,ObjSize
1.00,Gamma
Biggest frame rate hitters are the LOD and Object size options.
I run them both at 0.2 and get approx 50 fps on the runway.
May need to check but i seem to recall the Radeons are faster in DX9 but for DX8 they match the Nvidia cards.
Unfortunately AH2 is going to be DX8, whether this is the cause of percieved slow fps on Radeon systems remains to be seen.
However one oddity remains and that is the fps barely alters no matter whether resolution is 1024, 1280, 1600 or 1920.