If you want 4WD then the car will either have a manual or a tiptronic box wether its 2.7 or 3.0, but you can have a 2.7 2WD with the multitronic box, which is what I have.
For me it came down to running costs, I wanted a 3.0ltr 06-08, but when I looked into it the tax was about £450 a year for the tiptronic (which about 90% of the cars seemed to be) and I was worried about having to replace 4 tyres at a time due to the 4WD.
I test drove a 2.7 multitronic and loved it!
I ended up buying an 2.7 08 Le Mans Avant with the multitronic box and Im very happy with it.
However if I had the funds I would love a 3.0ltr!!