The 8 series a heavy and big car. Don't expect a same handling as a 3 series ! I have an 840Ci (a bit lighter than a 850Ci) Bilstein shocks and H&R springs, 275/35ZR17 on the rear and 245/40ZR17 on the front, but still there is that weight ... The M3 or maybe any 3 series with a modified sport suspension will probably outhandle the stock 8 series. Don't forget as many people already pointed out here many times , the 8 series isn't a sport car but a Grand Tourismo and what a fine example of that breed. SO try the car first and then buy it if you like, but do not exept better handling on tight curves than the M3 no matter what you do. Oke maybe if you'd spent about 10k on the suspension/wheel/tires then maybe ...