I think 16x AF is worth having because it filters everything but certain ground textures and has no performance cost. It does noticeably improve textures in some parts of the game. The only thing I've found to reduce flickering, shimmering and crawling of thin edges and lines in motion is downsampling. FXAA and MLAA don't do anything for subpixel aliasing as far as my eyes can tell, it's like having no AA at all in that respect. Just one of the failings of PPAA in general. So might as well stick with MLAA since it's less blurry than driver-forced FXAA. Maybe the difference is less obvious to you because you're running such a high downsampling rate, which I can't do because neither my laptop nor desktop (single OC'ed 7950) are powerful enough to do downsampling in Witcher 2. Without downsampling, no AA vs. FXAA/MLAA is no different as far as temporal instability of the image is concerned. But I still use MLAA as it handles all other forms of aliasing well while preserving the sharpness of the textures and keeping the clarity of the overall image intact, which can't be said for FXAA w/o downsampling.