Can anyone help with which of these is more important when working out anti-squat values? I'd discussed this on another forum and people had said that CC was more important, as IC was just a value generated by the links. Now, I'd worked with the assumption that when the CC was above the chain line, anti-squat would result. But looking at my graphs, antisquat doesn't come into play until after the IC has dropped below the chain line.
Is the axle rotating about the IC (obviously at an instant in time) or the CC?

IC is more important - the anti-squat calculation involves only this.

CC (center of curvature) is a point which describes the axle-path curvature at each position as if it was a circular curve (which is only true for single pivot frames).
CC's use is not that trivial, actually I don't really know why engineers use it. Probably it displays well the axle path shape details.