First off, thanks for that detailed explanation, learned some more.

Yes, the wall is 5 Blender units long, 2.5 from origin either way.  Its at about the 1.5 point that the distortion appears and goes to the end.  So that matches up pretty closely with what you are saying.

I tried scaling the marble up but that distorts it badly from its original form and it looks even worse in my opinon.

And yes the marble effects are pretty unrealistic.  I'm not a geologist either but I was a building contractor for nearly a decade and worked with a variety of marble.  Marble just does not look like that (maybe the closest to it is breccia capraia, which has a much stronger character and sharper distortions).  

And yes, I've UV mapped all the props so far and am working on creating bump and displacement maps, textures, etc for them.  What I can do with mapped textures is generally far superior to the Poser MATs I've seen.  My plans this coming week are to construct high poly versions of the same walls and use those to bake some really nice bump maps and textures right onto my low poly models which should make them look very nice.   I'm a bit behind however fiddling with this issue and also had some other things come up I needed to work on (who knew I'd be doing a bumpersticker for someone... but... if it pays... lol).  I still have the wrought iron gates to model and some smaller props.  All the rest of the modelling except the gates should go quickly, I'm still designing the gates.

But yes, I had noticed MATs seemed to work better on props that weren't UV Mapped.  I'm almost tempted to tinker with a version of the wall without a UV Map just to see what would happen.

Anyway, once the project is all done it then goes out to some friends for beta testing, make any adjustments based on feedback, then off to Rosity for product testing and if all goes well I'll become a Vendor here and have my first store item!   Wish me luck.

Appreciate all the input, I think this issue is about as resolved as its going to get unless someone surprises me.