I think I could hit 400 on a long road trip, but since my commute is mostly streets and congested highways I'll never get great gas mileage regularly. That's fine with me though, the X5 4.6 only gets 2mpg less than my 540i Touring so it's not that much of a difference in gas per week— maybe like $10 more per tank for the X5.

The 4.8 should theoretically have better mileage than the 4.6 since the N62 is a newer and more advanced engine with Valvetronic and full Vanos. The 6-speed transmissions helps with efficiency quite a bit as well. That being said, I'd rather have my much simpler M62 and 5-speed because I know them very well.

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2003 X5 4.6 | 2000 540i Touring

Formerly owned:
2004 Range Rover | 2000 M5 | 2000 540i/6
1995 750il | 2003 Mercedes S500 | 2003 540i/6