The PSS9 is a good setup, but it has one serious shortcoming. The front spring system extends below the top of the tire which reduces tire sidewall clearance by over 3/4". This prevents the use of 9" or 9.5" front wheels to maximize grip. A staggered wheel & tire setup is not the hot setup for track. The front tires are seriously overworked due to the inherent chassis weight bias (53F/47R). Big, oversized front wheels (facilitated by OEM perches or GC) address this issues and produce big gains on the 2 ton noseheavy chassis. The GC setup with similar spring rates will crush PSS9 on the track, if you swap 8 inch front wheels for 9.5's. The GC upper strut mounts with neg camber dialed in will allow even more grip.mikeoski said:Probably just in your pocket. The JRZ are about $200 more per corner. I would look into the Bilstein PSS9 setup. It is $1699 on Bavarian Autosport's site. You would benefit much more if you are looking for handling increase when driving the car hard.
I had the Dinan/Konis on my 540i, and liked the setup as it was much better than the soft stock setup. I am still running stock shocks/springs with the Dinan rear sway bar on my M5. It was just OK at Pocono Raceway last month. I am leaning towards the very adjustable PSS9 setup as other members who went that route have been quite happy.