One of the advantages of the cube environment texture is that you can blur it without increasing rendering time.
Use Bluroffset to unfocus reflections when using the cube environment texture as a reflection map to simulate unpolished surfaces.
The advantage to Cube environment maps is that they can be blurred as much as you want without any additional computing cost. When you generate a background from an environment map, the amount of blurring required to prevent aliasing increases with the field of view. In practice, very little blurring results when you use images with a 5122 texture and a field of view less than 90×.
For reflection mapped surfaces however, the amount of blurring depends on the surface curvature and the distance from the eye point. This cannot be computed automatically. Using the Blur_offset slider in the Blur window lets you unfocus the reflections by a desired amount (see Common Surface Texture Parameters for more information). In fact, soft-focus reflections can be used to simulate less than perfectly polished surfaces.