i cant understand why anyone would consider a spring kit instead of just going with a proper coil-over system. You are already in for so much on a hi end car, lowering springs are for guys on the GTI golf forums
A coil-over is a properly matched spring and shock and allows you to properly set up corner weights. Plus you can adjust ride height, rebound and compression and get teh handling as perfect as possible.
Lowering springs are too stiff and not enough travel for what the OEM shock is designed for and results in bouncy and less than ideal handling.