Moog LCA bushing, which one?

Im replacing my LCA to axle bushings and my local Auto parts store list 2 different Moog part numbers for my '90 XJ.

MOG K3131 (standard) $24.95 each

and

MOG K3164 (improved problem solver upgrade) $69.95 a pair

So what is this improved problem solver bushing? Is it worth the extra $20? I would go with more strength but don't want it to be polyurathane or anything stiffer like that.