Replacing your factory springs with lower springs and keeping your factory dampers is a bad idea. With 55k on your car, your original dampers are already on their way out. Installing a lower spring will only accelerate the decline in ride quality. If you want a lower car with improved handling, do it the right way. Replace the springs/dampers all at once along with FCABs and RTABs and whatever else is worn out.
1999 Techno Violet Metallic BMW M3
2005 Audi B6 S4 quattro 6MT
2004 BMW 330i
1986 BMW 535i