There are a couple of things to consider... Most folks who own the 4.8's are wanting sportscar like acceleration capabilities.. The 30si is going 0-60 7.8 seconds vs. the 4.8's 6.4... Big difference in the drivability of the cars... I own an X5 4.4 and an X6 50i... I have them because I tend to like to get from point A to B in hurry.. How long are you planning on owning the car? The loaded 4.8 will be an easier resell than the dime a dozen 3.0... Both are out of warrant so I would assume you are going to an aftermarket warranty either way.. kinda makes the mileage of them somewhat of a mute point.. Both cars under warranty the mileage will only come into play during the resell... if you are gonna flip the car in a year or two that would make the mileage difference a bigger deal... You only live once... get what you want vs. what would be the best deal....