I have driven the 535i and a 530D Xdrive and I was most impressed with the 530D.
Both where automatic. I would say a manual 535i is more of a drivers car than an automatic 535D.
I am also considering both since the 535i is less money than a 530xD.
I am quite sure that if you go for a quicker trip the Diesel will be much more economic that the petrol, a Turbo petrol can probably consume huge amounts of fuel when driven hard, whereas the diesel will still not be over 1L/10km.
A search in Spritmonitor.de reveals a 20% increase in fuel consumption on the 535i over the 535d:
http://www.spritmonitor.de/en/overvi...35&powerunit=2