Even full soft, the Koni Classic is going to provide more damping than a stock suspension firebird needs. The classics also have a digressive damping curve, compared to a progressive damping curve like the factory shocks or the Gabriel shocks.
If you like the somewhat floaty nature of the driving dynamics of a stock suspension firebird, you may not like the Koni Classic. It will seem more taught in normal day to day driving.
Here's a generic graph for visualization purposes. You can see in how the damping ramps how that might "feel" while driving.
The first gen firebird is woefully undersprung and underdamped IMHO but that's a different discussion. If you want the car to behave as it does from the factory, I do think the Gabriel is the better choice.