I drove both 28 and 35 with similar trim but on different time and location. To me the do feel about the same off the line; the 6 pot may pull little stronger on upper end but they are very close. I believe the 6 can do a second faster 0-60 but just doesn't feel it. The 8 speeds really help a lot.
To me the N20 is one of the smoothest and better sounding 4 pot engine but still can't touch with the BMW 6. I believe that is the biggest different between the two.
MPG is important to me and since I am not getting much option the xdrive28i is better deal to me.
By the way am I the only one getting it at invoice?