I too ran into problems with DX11. My game makes use of the Sobel post process effect and any time it draws in front of a plain black background (unlit material with emissive=0, or in front of nothing), like in this level for example…
…those static meshes were surrounded by a thick white line when I tried running the game in DX11. I never found out what caused it. I wasn’t doing anything that really needed DX11, so I left my own game in DX9. But if Coldscooter needs to run his game in DX11, I just hope he doesn’t run into any problems.