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the FSD shocks are going to feel softer than the bilstein lineup
the FE1 shocks are the factory "soft ride" option
The ride on our 2009 Z51 was getting too harsh on the bombed-out roads of Illinois, so I replaced the factory Z51 shocks with factory base shocks. That was a huge improvement in ride, but eventually I decided the base shocks were too soft for my taste.
I did a back-to-back comparison with another Z51 C6, so same suspension and even the same tires as ours. But he had Koni FSD shocks. They were a lot stiffer than our base shocks, perhaps not as stiff as Z51 but definitely too stiff for my taste.
Next set was Bilstein Heavy Duty (not Sports, which are about as stiff as factory Z51 shocks). They are on the car now, after about 15k miles they are a very nice compromise. I'd say about half way between the base shocks and Z51/Sports.
We are very happy with the HD's, but your situation may be different.
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