There's some very useful information here, thanks guys. But it's led me to have more questions, if you don't mind.
For A, or in thinner clusters, is it better to use AA or to dither?
And for B, Jad mentioned how 25% dither looks shitty unless it subtle. I think that's a pretty universal feeling, although I hate 50% more if it's not subtle. But my question is, if I only have those two colors, is it better to make a 50% dither cluster, and then dither between all 3 or to do a straight gradient? A better question would be, what's the best way to create a subtle or unnoticeable dither with very few colors?