For real world driving 2nd to 4th are the most usable, but as Ken says, waffling along at 50 to 60 the auto version is probably in 6th, giving close to 30mpg...
Having done long journeys recently - a steady 70-80mph cruise returns 33mpg
If driven on the low-end torque the economy is pretty good - mine has averaged 26mpg since I got it at the end of March.
