As I mentioned aboth, my GPU can run BF3 and other performanceinstensive games with out any problems, so that really shouldnt be the problem.
I reduced my CPU side stuff because I was certain that the problem lied there. My pixelshader is fairly simple, and there are not THAT much pixel beeing processed multiple times.
I can't say that I have a clue what the 3rd thing you mentioned is, but I will go ahead and research.


I noticed something wierd. When I draw 9x 256*256 instanced without height, shadows and normals passed to shader, the performance sinks down to 10 FPS/ 100ms,
when I draw 36x 256*256 with a normal drawcall for each (and normals etc. send to the shader), I still remain with 50FPS/20ms. By changing the pixelshader to return float4(1.0f...); I don't get a performaceincrease.

I came up with another question. When the window in which direct3d is drawing has not the focus, which influence has this on the performance? I noticed that in many games the FPS go down to 10 if I focus another window.
I got a console for my application, so I can output things for debugging etc. Could this have influence on the performance?