Well if you aren't already aware BMW is offering 0.90% financing on 2006 models if you are going that route. Second, there is the CPO warranty on them that is 6yrs/100K miles from when it went into service---so the '06 you would probably have about 3 years of coverage. Now if you are wanting a warranty past that there's been a couple of threads on here about warranty companies you can just do a search.

As far as which one I would go with the '06 because of the extra year of CPO and the lower miles for basically the same price (and of course try to get them to come down a bit on it). The "buyback" on Carfax I'm not sure what that entails but maybe the dealer is right---I would research yourself or someone else on here might know more.