I think this image speaks for itself regarding microdisplacement and different shader roots. Using a different root doesn't change the issue, to get fine scale displacement you need a lot of polys. Which means either a detailed object or a lot of subdivision. (In this case I used the Ball primitive which is pretty low detail, simply for the sake of a clear example.)

Here are the shaders, which I kept as simple as possible (with a single infinite light so that it would be the same on each object). PoserSurface:

PhysicalSurface:

Cycles:

Note I've plugged the displacement info (a Marble node in this case, but could be anything) into a cycles Math node. Varying Value2 will increase or decrease the amount of displacement, so that's an easy way to make it adjustable. The amount isn't exactly the same as the PoserSurface and PhysicalSurface in this case but I think I have it pretty close.