The Impala SS, being of the same chassis "class" as the original 91 "whale", had the -1516/-1517 shocks "qualified" for the application. These shocks use digressive valving, which equates to softer under most conditions. The -1517 rear shock is longer to allow easier removal of a rear tire.
When the body was changed in '93, this opened the door for Bilstein to consider listing the previous (box-car application) -1104/-0929 linerar-valved shocks as a more aggressive alternate, especially with the lower ride height of the Impala SS, which some lower even more. The shock length is probably more of an issue on front than rear, but most who have tried them seem to favor the early design over the later shocks listed, and Bilstein decided to call the early shock(s) a "Sport" application for the Impala SS. The OE deCarbon shock is a pretty good compromise in this area, actually, but they do cost more to replace than using Bilsteins.
A front shock that might be worth looking into for the front of a lowered Impala is the S10 Extreme/ZQ8 shock, which is also a deCarbon item, that I think is a little bit shorter than the OE Impala shock. Rears are another matter, but I think I prefer the -0929's, as a starting point. Others like Koni, HAL, etc....I'll dig up the GM P/N's for the front S10 shocks if anyone wants them.