I drive a 2001 3 litre Z3.
Good points: Plenty of torque, superb engine and gearbox.
Negative: Understeers when on/near the limit, traction control too intrusive.
Smile factor: Gorgeous over-run, M5 wheels, Full M Sport spec.
Niggles: Looks dated compared to the Z4, not the best build quality.
Running costs: Servicing/new set of tyres P/A = £1000 PA
Buying: Go for the straight 6.
Hope this helps.