I think the Whiteline poly inserts are a good stop-gap that are pretty easy to DIY. I started with them because they were like $45 and an evening in my garage after work. I waited until LSD install for the full polys and had a shop do the work. It's hard for me to imagine a need for anything stiffer, at least not for the street. And I haven't noticed any increase in NVH or squeaking or anything.
It's difficult to overstate how improved the car feels with upgraded rear subframe bushings and an LSD. Like a proper sports car. I can't believe the garbage bushings the car shipped with. No matter which option you choose, it will be a great improvement over stock.
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