Depending where you are in CA you I would drive both power plants. The X5 is more weight and I opted for the 4.8 for it's torque. The sound is a nice bonus. Since the option price list is different for some options for each model you need to play with it.

For a sedan a turbo six sounds great but I am very happy with the 4.8. Comming from a turbo they do not exactly sip gas either.