shocks should be matched to spring rates for optimal ride and handling. I learned this when I messed with shocks on my touring motorcycle (a BMW R1100RS). stiffer springs require stiffer shocks. The better motorcycle shocks are highly adjustable, with both low speed and high speed rebound and compression damping all being separate settings, springs adjustable for preload height, etc. a couple cars ago, I upgraded the springs to a HD spring in back, and shocks to bilsteins, someone loaned me a spare set of TC and SP bilsteins for the rear to try before I ordered mine, and I settled on the TC (which I think are now the 4600, they were called 'touring' back then).