So I need to know if I'm wrong about another difference between bump and normal.  Since normals refer to the perceived angle of the surface perturbation, and use RGB colour space, I had believed them to be more accurate.  I'm using a displacement map in my project, and it works very well for things like insets and frames.  But if I try to make a smooth bulging window for example, I get a lot of stair-stepping.  It seems like each level of grey "plateaus" when micropoly displaced,  rather than producing a smooth shape.

I thought of using something like ShaderMap 2 or xNormal to convert the displacement to a normal map, but that wouldn't solve my problem would it?