Delrin leaf spring bushings

When it comes to leaf spring bushings for handling and performance what's the general concensus? Urethane front eye and rear shackle? A mix of urethane and rubber? Has anyone tried Delrin bushings (or are they even available?)

The reason I ask is because I came across this company that caters towards 2nd gen camaros http://www.customworksperformance.net/suspension.html towards the bottom of the page they have an interesting setup when it comes to the leaf springs. They recommend a delrin bushing in the top of the shackle and a rubber on the bottom of the shackle, has anyone tried something like this on their mopars?