coil-overs vs. springs...depends on what your gonna do.
my brother and I went from Carl's HD spring set to Irelands coil-over set once we started tracking...there's a major difference!! High speed cornering HD spring will produce a lot of body roll & wheel lift, coil overs will flatten it out....for a price.
If your not gonna track, Carls set up is real nice, if your gonna track it, you'll learn the difference. Coil overs can be tuned down for the street with different spring weights.
We run 550lbs springs up front (IE coil-overs) with 500lbs sprngs with Bilstiens in back in our coupes. Kinda harsh on bumpy/crappy roads, but AWESOME on track or nice pavement/freeways...they turn e9s into go-karts!
But if you are considering coil-over's, look at the complete suspension pkg, ureathane bushings, et al...
HTH-
-shanon from the Essex Flying Circus
-73 E9 3.5L dedicated track car
-70 E9 3.3L track/road car
-2x 2002 racers, one competed/finished the 25hrs of Thunderhill Enduro