if you can get an Aston...get it, that seems like a no-brainer to me. A M6 is a common-exclusive car, same as the 997tt, but Aston are rare and they look great, in this league practicality should have very little to do with the decision, so it's pretty simply buy what you really like

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2006 BMW X5 4.8is Lemans Blue/Beige/Dark Maple
-Nav, Comfort Seats, Heated Steering Wheel,
Rear Airbags, AUX Input
2009 BMW M3 Space Grey/Black/Carbon
-all options