Picking up my 08 4.8 this Thursday should I go through with it?

[np2004]

I still am debating on whether I should pick up my 08 X5 4.8 this Thursday because of the possibility of the twin turbo 4.4 V8 from the X6 replacing the current 4.8 V8 in the X5 very soon since it would have more hp/torque and better gas mileage. Also with the thought of Performance Dynamic control being included in the 09 X5's. What advice,comments, and words of encouragement can current and future owners give me on what I should do. If it was a lease I wouldnt care as much but since this will be a purchase what suggestions do you offer?