I installed a set of Bilstein rear shocks today which I purchased a couple of weeks back. I upgraded the front shocks to Bilstein's earlier this year but waited on the rear shocks as they are a little expensive.
The front Bilstein shocks were dramatically larger than the KYB Gas-A-Just front shocks. The rear Bilstein shocks are also larger than the KYB versions but the difference is not as dramatic. The KYB shocks can be compressed without much difficulty. The Bilstein's seem to be about twice a stiff.
The Bilstein rear shock is shown below with and without the boot beside the KYB shocks they replaced.
This is what came in the package provided by Street or Track. They were $94 each.
The replacement of the rear shocks does not have as much impact on ride quality as when the front shocks were replaced. I can tell the car rides better. When there are a few people in the car, the back will bottom out with 4.5 mid-eye leafs. I'll need to replace them at some point but I'm curious if the stiffness of these shocks helps the situation at all. Time will tell.