HD and Sports have same valving rates,
difference between them is ride height compatability
I got away with HD fronts and Sports on back when installed M3 springs onto my 87 325iC
can't complain, great for everyday driving., she's on 225/50/15 and it's a bit heavier than coupe and sedans. got springs from www.s14.net
for $ 75 shipped.
for oem height or slight drop as with M3 springs
for after market springs like Eibach, H&R, IE, etc.
most ppl prefer H&R + sports, good lowering stance, a compromise between street and track duty.
Stage 3 (made by Eibach) are stiffer yet, and, recommended for track use... found here http://www.bmw2002.com/
Eibach Pro Kit
lower ride height but offer almost OEM feel, great for smooth country roads while not sacrificing ride plushness.
As far as replacing SF bushings, do a google search, there's tons of write ups about it.
most guys torch them out and then Sawall whats left., not my coup of tea, but that's how most ppl do them.