Anti aliasing is really a throwback from older technology... Back when 800x600 was high resolution... To get smoother images you need better resolution, but you're stuck to the monitor technology of the time. So they came up with a way of smoothing the image across existing pixels to make up for the lack of real physical resolution.
Nowadays, though, with ever increasing resolutions, HD, and so forth, you only benefit from the lowest setting to just "take the edge off" of the image on the screen. Maxing out FSAA doesn't really help all that much. I've gone through every setting my video card has and in the past tried numerous driver versions and makes to test them out... Never could tell the difference between 4x FSAA and 16x. Never could tell looking at the monitor, that is. And that's really the important thing.
Turn it up to 2x or 4x, then stop there. No benefit at higher levels.