I tried the 4cyl spring setup, and i hated it. Car was a sloppy mess to drive. I don't know how long you been running lowering springs and how much you drive the car, but i would not recommend the drag setup for anyone that isn't 100% dedicated to running the quarter.
I couldn't adjust to the new setup, every corner felt like i was gonna crash.
I'd rather run the 1/4 .3 slower than drive around that way.
i as well tried the cheap 4 cyl spring set up with the front sway bar removed and it SUCKED my tired ended up shredding from the wheel wells hitting the wheels all the time. i missed my lowering springs. I heard that the "other" drag springs are better, but i have also heard that you can hook up pretty well with the right setup and lowering springs. ive been out of the mustang scene for awhile but i KNOW this topic has been covered on here before (probably by me in the past)... do a little research and youll be amazed what youf ind...
I still had my sway connected, and it was still a wreck.
Only thing the drag setup on the street seemed good for, was the shock value you got out of stepping on the gas with a passenger in the car.
I use koni adjustable up front (on the soft setting) and qa1 12 way adjustables in the rear. Pretty much lets you setup the suspension plenty good with lowering springs.