FXAA does not need optimising, its a post process effect afaik.
Yer it is and it was probably AMD not optimising so well in the rest of the GameWorks libraries. Remember that Warner Montreal refused AMD any code for Batman AO and this could be the reason. It doesn't explain why the gap is closed so much when MSAA is used either (even though MSAA is better on AMD HW). The fact remains that MSAA is the best looking and FXAA is nVidia's own tech (Like MLAA is AMD's but nVidia didn't close it off unlike AMD did) -
Just sayin
