Been running my BC(V1) coils for a year now. Occasional trackuse last summer and a bit of icetrack-racing this winter. And mostly street of course.
Took a while to get adjustments fine for street, I think the 8/6 springs are a bit hard, at least for our roads here in Finland(probably the worst roads in europe). But putting the shock settings to almost the mildest position they are drivable. Drivability is great, comfort not the best one.
For track use they are great, at least they are not the weakest link in my setup, my tyres and the body is giving up way before these coils do. Feels like the rear end of the car is twisting(and it probably does /ubbthreads/images/graemlins/laugh.gif), but traction is good. For a sunday trackdriver these give much for the money, for pure streetuse, I would recommend something else, or try different springs.
Oh, and I had a terrible clunk sound coming from one strut after a icetrack-session. Took a while to find out what it was...a loose nut in left front shock upper mount. After tightening that back and all noises went gone.