Re: H and r super sport springs??
I have them on my 03 v6...basically the same stock suspension as your GT. The H&R's will lower the car ~1.6 in the front and 1.75" in the rear.
That's with the stock isolators...taking either top or bottom or all out will lower the car more.
The ride is stiffer and louder, but I do not have any isolators and 315 rears.
If you go with Super Sports you'll want to get CC plates and a bumpsteer kit at minimum. New shocks/struts, ball joints and isolators should be bought if you have higher miles (+60k) or if your shocks/struts are noticeably worn.
Keep in mind the more aggressive spring rate will cause stock components like shocks to wear faster than normal...also a lack of proper alignment will cause accelerated and uneneven tire wear.
12 Black GT500 SVT PP l 2.6 Pulley/Idler l Airaid l o/r X l 305 NT555R's l Recaros l
04 Azure Blue Mach 1 / 03 Sonic Blue 3.8 / 14 Sterling Grey F150 FX4 402A 5.0 / 11 GT500 R.I.P.