We just bought a 2016 3.5 xdrive X3 or whatever they call it. Dimensions are very close to the e53 X5 we have but of course it is a little less powerful than the 4.8is. It is very smooth, drives great and has plenty of room for our lab - but we don't have your commitment to dogs. I owned a 2004 X3 (first year) back in the day and it did real well for us. I have no reservations about the X3 if it fits your needs.

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Mike

2005 e53 X5 4.8is 169k miles
2018 f90 M5
2018 Volvo XC60