Someone asked why 80 MPH+ is the TDI's sweet spot. It has to do with the engine's efficiency at a certain RPM, and since the TDI has an abundant amount of torque at a relatively low RPM, it can sustain high speeds in a higher gear with ease. The PD adds an even bigger advantage in that it seems to rev smoother and faster thus broadening the power band even more!
Our 2004 Passat, once it slips into 5th gear and the convertor locks up, is turning 3000 RPM at 98 MPH! And it will pull a hill like it it's not even there without a hint of a drop on the tachometer. On level ground, at 80 MPH, the MFA reports and instant MPG of around 44 MPG, and it feels like you could get out and walk it is so smooth!
In contrast, a 2004+ Lexus ES330 (I pick this car because I am familiar with them) is wound up to about 3200 RPM at 80 MPH, and its aluminum V6 is whining like a chainsaw...you definitely can tell you are going fast..and its instant MPG meter shows around 19
It, too, uses a 5 speed automatic. Not sure about the acuracy of the mileage meter, but our Passat is running about 2-3% optimistic. Even taking that into account, there really isn't any other mid-sized sedan sold in the US that can claim what the Passat does, unless you include the MB E320 CDI at nearly double the cost.
The TDI is just a magnificent little engine!