If the material is for LightWorks, I'd use Color Class Shader "Plain" to match the color of the sample and add a little Displacement Class Shader "Rough" .01, .01, 1, 1.
For texture maps in general, the smaller the better.
This is addressed in the "LightWorks in ArchiCAD" book on page 110-111.
Larger samples take more time to render and consume more RAM, but even 500x500 is not large.
Dwight Atkinson