I agree with 16's for heavy city driving, but I'd expect 10's-11's for highway; but then that would assume cruise control most of the way.
As I've said before in posts on this subject: Prior to the D3 I had Subaru Liberty 2.5's and no matter how hard you drove the econ would be the same, 10s (My manual '98 2.5 liberty was the best car I've ever had:D:D:D, better than the 2005 2.5i) .
The D3 with the Ford V6 is not the same beast:(; I've had to completely re-style my city driving to slow acceleration (revs <= 2700) and to anticipate braking. Doing this I've dragged my first few months with the D3 from 19s to 15-16s.
Keep in mind though the D3 V6 should be measured on the diff between say a Falcon or Commodore V6 and the D3's figures with 2.7 ton to drag around.

