I dont have any experience with 170 or a quattro version, but I have 2.0tdi 140 DSG leon a good few years back and even hooning it around like a loony hard acceleration and high speeds on the mototrway it was almost constantly in the 40+mpg means you get more like 450-500 miles out of a tank!
One thing I will say is it isnt nearly so much fun, and the extra weight over the front wheels does give a strong tendency to under-steer, used to get ESP kicking in on small round-abouts when pushing on.
If your even going to consider it, then I would suggest a quattro version would be a necessity to help kick some of the torque to the rear wheels to help with the under-steer, and I personally would never own a diesel without a decent auto box as the shortened rev range makes it very un-sporty. Just my opinion mind!
I would also strongly consider trying to get one of the new CR engines as the refinement is quite amazing compared to the previous PD units.