What video card do you have? I use High Quality with a high end card.
Here is a tweak guide that explains some of the various settings.
http://www.tweakguides.com/NVFORCE_6.html
"Texture Filtering - Quality: The available options are High Performance, Performance, Quality and High Quality. This setting determines among other things the level of Anisotropic and Trilinear texture filtering optimizations applied by the Forceware drivers. Generally speaking, the High Performance setting enables all optimizations, meaning slightly lower image quality but the highest level of performance. If you select Performance, some optimizations will be disabled, progressively more if you choose Quality. If you choose High Quality you are assured the...