The image on the top left is a render from 'Mei Omei' rendered at AA6 GD7 which took 11m 47s to complete the small 340x200 image. The image below was rendered using AA4 GD3 and took 2m 12s almost six times faster with no real difference in image quality.

The images in table below are all from the area marked in red but rendered with all the combinations of AA and GD. I stopped at GD7 as in my experience there is very little point going higher as the increase in render time gives little or no visual improvement to the image.

Although the very highest setting (AA6 GD7) here does show some fine detail to the 'sand' it comes at a price of increased render time at 1m 32s. Whereas AA4 GD3 gives and almost equal result but with a significant saving in time at only 28s almost 3 times faster and if we were talking of hours or days instead of minutes the time saving is so much more significant.

The two images marked with a red dot are oddities in that they rendered faster than would be expected, I actually ran these two tests again just to confirm the results were not mistimed.

Settings of AA0 and AA1 render in exactly the same time with a fairly noticeable improvement in quality but no increase in time. So from this it seems pointless ever using AA0 even for rapid render tests.