Not sure if serious. AMD has had SSAA since the 69xx series, what's so new about this?
4x RGSS looks better than anything else IMO (as long as the texture LOD bias isn't set low so that there is general texture shimmering). I've never seen a need for non-Rotated grid sample patterns. 4xRGMS is also good, but it doesn't AA the whole image.
I also am not sure why people are so worried about performance.