I am sure you are aware (and as Clayton sort of hinted at), the rear suspension is really better suited to rod end / heim joints rather than bushes of any type as the pivots roll through differing axis so, they will always strain and deform a bush.
For example, when my car was built originally the poly bushes were worn out before the car was even driven due to deformation with the rear suspension at full droop during the build.
I would expect a solid bush such as delrin, bronze, etc, to be even worse as there would be no give at all through the suspension motion and would actually strain the mountings and fasteners.
I changed to rod ends which removes any binding, allows the suspension to work better and the amount of noise / vibration difference is barely if at all noticeable.
Worth considering from my point of view.