Don't know about the spring rates but I've read that the turbos do have beefier antiroll bars. Some people have installed them on their non turbo cars to get better handling and flatter cornering. Manufacturers tend to assume that people buying turbos are performance minded and desire a better handling car. In the age before dynamic computer controlled suspension tuning it was an all of nothing sort of thing. Couldn't have soft cushy ride and good handing at the same time.

All my bricks, 200,700,900 series ride pretty good on relatively good pavement - giving a rough ride to REALLY bad on a choppy interstate not far from here.

On that section of road, the 940 does best, the 245 next - the 760 worst. In fact I have owned a number of 700 series, and they all handled rough roads badly.

I did have a 720 wagon, and the front shocks had actually partially frozen - not moving freely - making for bad ride all the time.

Never replaced any springs, but I am sure that should be considered in trying to get the best ride you can get.
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' Of all bad men religious bad men are the worst. '' (C S Lewis