The 06 with freshened air system and preventative maintenance is a no brainer (the other car is just at the mileage where it will prob start needing that air suspension stuff...). Just having maintenance records tells you a lot about the owner imo (that they care, that they are organized, that they can afford to fix it when it breaks, etc) so that's a huge plus for that car. Plus the comfort seats are AMAZING. I thought I wanted sports seats, until I sat in the comfort seats. You have the E39 M5 for sporty driving and it's sporty seats. The X5 is fast but also comfortable, and it being an SUV you aren't likely to corner it the same way as a sports sedan so you don't need all that bolstering to keep you in place in the corners, so imo the comfort seats fit the nature of the car.
Plus its cheaper and no taxes as its for sale by owner, bet you can even get them down on price a bit.