Need help deciding btwn a 2008 3.0 or 4.8

[np2004]

I am in the market for a 2008 X5 either a 3.0 or 4.8 to compliment my 2004 330ci. I have a few questions for those with either model. What kind of realistic gas mileage can I expect from either model in the city and on the highway? How much of a difference does the 90hp make in practical driving situations in the 4.8 versus the 3.0? I have heard the 260hp isnt enough in the 3.0 when you push the truck. Is the premium sound package really worth the $ and does it sound that much better than the standard system? is the technology package worth it? I have heard the back up camera doesnt work well at night so I am thinking of getting the navigation system as a stand alone option since its a must have option for me. In general what are the pros and cons of the 3.0 versus 4.8 from current owners?