My personal experience.
I have a R31 skyline, Silohette, Series III. (its a live rear end). I knew my shocks were hammered when one of them broke in half and supported itself a while on its mount but later fell off. Made it look like a pimp car.. I noticed I had 3 diffrent brands of shocks on my car, and the rear seemed to have towing springs.. way high. I needed the full treatment.
Any way, got Monroe GT Gas shocks, and I belive Lovell springs fitted (1 1/2 inches lower). Sensor track apparently was avalible at the same price, but was pointless on a skyline.
Any how, Im happy with the suspension, it scraps a little on steep carpark ramps, but thats the only place. The ride is firmer, but not bad, even with high psi tyres.. Perhaps I could have gone with a firmer spring or shock.
From my experience:
-Don't goto pedders unless you can handle them, thier bull**** and you know exactly what you want.
-Avoid other big chain places
-I visted unquie autosports, lovely bunch up there, gave me a great price, advice, namebrand stuff, but when I asked how long "Oh we are really busy, 1 or 2 months". I needed it now. However they knew stuff. Find a enthust type shop.
-Don't cut springs, or heat them up, everyone I spoke to (machanics/mates/tech heads) said bad idea. Besides keeping the origional springs may come in handy.
-Don't go lower than 1 1/2". Otherwise everyday driveabily will be buggered. Also handling on some rough roads will be crap too.
Right now Im please with my setup, if I had my time again, I would have tried harder for maybe a 1" drop and some firmer/better shocks.