I'm trying to achieve a scratched surface effect using a bump map, however it turns out the surface details are not preserved at a distance:

The first picture shows the metal part at high resoltion, the second picture is a down-scaled version of it and the third picture shows the same part rendered at a distance. I tried the options for texture filtering in the Image Texture node, but neither linear, smart or cubic provide good results.

This surprises me actually because Cycles obviously does supersampling for the primary rays, however it seems that it downsamples the textures on the fly or pre-calculates mipmaps instead of sampling the textures at full resolution.