[BonzoHansen]

To the heart of the matter, it is echoed in books like Herb Adams' Chassis Engineering. It's all about the bind, and to a much lesser degree the way it wears. WBT I bet your local library has a copy, it's a terrific book. That said, a poly with a steel insert that is greasable at the pivot point is different from a pure poly bushing.

IMO poly is a step between OE rubber and solid racecar type stuff. With the advent of solid stuff with delrin inserts for a street car you get much closer to the best of both worlds, without the inherent noise and wear issue of actual bearings that are not weathertight. For a pure street car a higher durometer solid rubber bushing is likely an excellent, perhaps cheaper, upgrade.