I measured an
Eibach variable rate spring (what I have on hand) for the stock
suspension at 15.2lbs. A 475 lb/in coilover spring weighed in at 7.2 lbs. (I'm currently running 450 lb/in springs but the difference in weight will be negligible, maybe 7.1 lbs?) The stock shock weighs 2.6 lbs while an aluminum coilover (that is much longer with a much larger diameter shaft) weighed in at 4.0 lbs. Not only is there still a net reduction in unsprung weight of 6.6 lbs, how it is loaded into the chasis reduces the flexing of the shocktower. In the stock
suspension, without a monte-carlo bar and export brace, every time the
suspension goes into compression, both the caster and camber change slightly. The binding of the stock spring perch creates a sudden change in the wheel rate and a hammering effect on the shock tower. Without the Shelby drop, the instant center is somewhere in outer space, so there is huge room for improvement.
I'll go out on a limb and say that any of the coilover set-ups available that mount an aluminum body shock on the outboard of the
LCA with an appropriate spring rate, will have a noticeable improvement in handling quality over a stock style
suspension with any number of tacked on upgrades. If you don't intend to take it out on the track, you can pick your favorite color: TCP is blue, GW is red, RM is silver, UP is dark grey. If you want to push the envelope, the RM kit should be the lightest and therefore most responsive. If a c/o is out of your price range, you can still make huge improvements to the stock layout, just remember weight is the enemy.