the last dithering post seemed a little overworked & I hadnt heard of anyone testing these out:
AMD/Radeon cards give you an option to turn off dithering when using a displayport cable. Just pick 6 bit vs 8 bit output and you'll see the difference immediately. There are also several other options you dont get with nvidia like 4:2:2 chroma. They dont seem to do the trick for me, but maybe they will for some folks?