Just installed Dinan springs on my 550 xDrive, and had Stage 2 previously installed. NOW it drives as it should: turn in is precise, no plowing on braking, flat acceleration. It's not an M (have an E46 M3) but it is a monster that now does what it's told.
I'm a big Dinan fan. Yes, they cost more. But it amazes me when a BMW buyer whines about Dinan cost. His product is superbly engineered, and that's what drives my selection. Are BMWs over priced? If the answer is Yes, then buy a Lexus. Or worse, a Mercedes. Why worse? Cost as much and engineering is a necessary challenge, not a goal.