Antialiasing : a technique for smoothing out jagged lines in graphical computer output.
(this just helps the edges of letters and pictures look smooth)

Anisotropic filtering is a method of enhancing the image quality

not really sure what Extention limit is, but I did a search and found that most people keep it off.

I don't believe Antialiasing and Anisotropic filtering will effect your system performance.

unless you're a gamer I would just leave them at their default settings