The Normal Version has an Average Texture Resolution of 2048x2048, with Full Res Speculars and Normals. It will make your game look Fantastic, and it's barely a performance hit for many users. It only has one file, and no requirements.

The Ultra Version is Extremely High Res and Future-Proof. Its Average Texture Resolution is right around 4096x4096, with Full Res Speculars and Normals. This version requires the LAA (Large Address Aware) patch.