The Sach's kit will probably be your best choice. I put one in my old 535 about 5 years ago, and with the 17" wheels, the ride was much firmer than stock, but the handling was great! Due to the firmer suspension, your brakes will even seem to work better. I did find out later, when I put a set of 16" wheels on the car, that the ride was much closer to stock with the benefits of the lowered look and much better handling.
I would recommend the Sachs system, along with new thrust arms and control arms and any other possibly worn suspension component while you are in there. There's nothing worse than doing the job twice. Someone posted that the price was going up soon also. I believe it was around $635 shipped, going up to $675....when I bought mine they were $730 shipped.
Jr
'91 ///M5
'91 318iS