Thanks to Taz for his incredibly informative posts in this thread. For sure, if the vehicle will spend it's life only on a race track, than the bushing choice is an easy one to make , but if a vehicle will spend most if it's time on the street, then just how much vibration and harshness are you willing to put up with? In my mostly street driven mustang cobra, I replaced the front hydro bushings with poly versions and right away, I noticed the increased harshness. The harshness was not terrible, but it was very noticable at low speeds( 25-40 MPH) on rough roads. I had the chance to drive a mustang with Delrin pressed into the stock front conrol arm bushings and in my opinion, the front end NVH in that car was unaccecptible as it was significantly higher than it was in my car with the poly bushings. The IRS in my car is currently stock as I think about getting the slop out of it, I do not want to make it ride like a truck because first and formost, I drive on the street, not the track. Everybody is diffrent in terms of how much NVH they are willing to put up with so I will be conservative with my bushing choice. By the way OP, nice work on the powdercoating!