Zell - I went with the polyurethane RTAB to avoid having to do the preload setup required for the non-poly RTAB'ings. It was a "chance" I was willing to take to avoid the extra effort and chance of screwing up the preload. I'm sure any new RTAB is going to make a big difference which was more my point with respect to the RTAB rather than it was the "poly" RTAB that made the specific difference. In saying that, I definitely don't regret using poly RTAB's as I have absolutely no complaints.
There seems to be a lot of debate about the polyurethane bushings being louder and harsher than the rubber ones. IMO, I think they are slightly louder over rougher roads (I image the noise would be more pronounced over concrete interstates), but not necessarily harsher. Instead of harsher, I would call them "firmer" in their response to bumps. Now this could be because the Koni FSD's take up the "harshness" and turn them into "firmness", I don't know, but I still wouldn't call them harsh. It is really difficult to confirm given all the changes to the suspension.
BWOODM3 - I purchased the parts from a number stores as no one store was the cheapest. There are a number of forums on here which lay out the list of parts depending on what you want to do. From there, I just did searches on the parts, but ended up using Bimmer World, ECS Tunning, and Pelican Parts.