My experience is that, in stock form, the suspension and handling of the S550 is not comparable to the S197. It’s much better.
And for its part, the S197 is a way better handler than the Fox body was.
My 2015 was a base GT that was born with crappy 235-50-18 tires.
So in my book, what I did is a major improvement. Both suspension and tires.
I deliberately went to 265 in front so they would not be so wide as to cause much or any tram-lining.
I’m very pleased with the results.
Been driving it since 2019, so I’m sticking with it.
Can’t say I have complaints about the Shelby handling either, except occasional tram-lining in heavy truck ruts.
But that’s caused by the wide front tires, not the rear tires.
And my 2006 was also a regular GT when I got it. There was no performance pack option back then.
It was born with crappier “17 inch tires than the 2015, so I feel going to the GT500 setup of back then, along with suspension upgrades, is also a vast improvement.
That is 255-45-18 front and 285-40-18 rear.
I’m happy with all three cars.