question about rear springs

spankmeister7 said
My car is a 1965 Barracuda.

Sooner or later I'm going to add a set of anti-sway bars, good ones, to help a bit with handling. While researching the topic I found that the Formula-S package boasted stiffer rear springs than the standard version of the car.

This may seem like a basic question, but what's the point? I mean, exactly what benefit would it give to the handling of the car? I'm asking because my springs are sagging a bit and before I replace them I'd like to know if I should get the same stiffness as it was originally, or add stiffer springs to the vehicle. I'm also curious about how it was made to be stiffer. Just an extra leaf? Or perhaps it was the bend of the spring.

I'm not at all interested in going for a raked look. The much larger rear half of the car already creates this proportional look to my eyes. My Barracuda will only ever be a peppy street car, but there are lots of curvy roads around here that I fully enjoy driving on.

The point is that when you take a turn on one of your curvy roads, the body wants to roll over out of the turn. A stiffer spring pushes the body back up as the weight shifts, and that in turn helps to plant the inside rear tire into the turn. Without the stiffer springs, the harder you turn the easier and quicker the body will roll out. Too much stiffness will cause the wheels to hop, or loose traction. A turn must be fluid and the body sort of flexes or finesses its way through the turn. These cars have a very high center of gravity. The flatter you are going into the turn the better. The tuned stiffness of the factory springs will make cornering much more comfortable. The anti-sway bar will also help pull the opposing side of the rear down as the car leans over.
Without a doubt keep the stiffer prings, and have them re-arched, or buy new ones that are tuned similarly.