i seem to recall it as having changed for different model years. some years SS being top dog, others the Z/28.
when i think of the SS i think of a powerful engine with the creature comforts, the stuff that puts a little more luxury on the inside of the car.
Z/28 to me says Bigger engine than an SS, and not so many comforts.
who knows, maybe i'm terribly wrong and mis-informed.
but either way....
that car is the definition of awesomeness.