From the OP's description of the type of journey he is doing and bearing in mind there is no traffic, in the 330d I'm pretty sure I could get 50mpg +.
So, a 335d would probably be 45 mpg?
But, obviously I'm biased, however I think the 330d would be the better buy because its cheaper to run but still very rapid, especially when compared to the 318d.
If you look in my gallery you will see proof of the sort of economy that's possible with the 330d
