Been curious about these myself. The spring rates look decent as they are on the soft side. What i would be curious about is the rebound. Also like Ironsnake said, the Raceland kit is the same and much cheaper.
As far as spring rate goes, I can tell you from experience its a soft kit. You can try to bump the overall spring rate by changing the springs. But I wouldn't considering the shocks/struts aren't really prepared for that. A friend runs a BC racing coil over kit on his 95 M3 that I installed and it was of better quality and stiffer. The performance of the car itself was pretty spot on considering its price point (1000). It's up to you what you're looking for in a coil over kit but you can use different manufacturers front and rear to achieve a better result. I'm using UPR's kit which utilizes the standard eibach coil over spring. I can swap it out as I see fit. This is over a bilstein strut.
Personally, if you want a one stop shop, buy the BC if you're against say Maximum motorsports because of price. I would always recommend MM for their quality. But even I can't afford them all the time. If you're looking for a universal setup that you can change springs on, something like UPR's would be the right direction.
Thanks IronSnake.
I have Steeda sport springs on it right now which have a sprig rate of 650lbs front and 250lbs rear. The stance is right where I like it but I find it too stiff as daily driving. I don't do Track, racing nor autocross. Just trying to enjoy the ride.
I've intalled a Megan Racing coilover kits on my son's Stealth TT and really like the ride.
In short I'm just trying to get back at what the stock Cobra would be without the 4x4 looks.
Can't say much on the quality of the SR kit, but as far as springs rates go I have the MM kit on Koni yellows in the front using a 300# spring. Its pretty stiff for my DD liking, thinking of going down to a 250# spring.
After looking at different sites (Late Model, AM, Summit, etc), I found these
Ford Racing Lowering Spring Kits M-5300-B http://www.summitracing.com/int/parts/fms-m-5300-b/overview/
And according to comments; this is what I'm looking for:
"I wanted a spring that didn't lower the car too much and wasn't too stiff. These springs lowered the car perfectly"
"These are a great spring. Very close to stock ride quality while lowering the vehicle enough to look good."