The V70 is going away for the USA market, just the XC70 in 2013. The larger 3.2L engine does take more fuel, but it is a pretty good compromise with power and torque. Finding a V70 with the 2.5L 5 cyl engine is getting harder if you are looking for low mileage and pre-2008. The EPA fuel figures are pretty pessimistic and you should do better than that, figure about 20mpg around town and mid to upper 20's on the highway with the 3.2L.

You cannot compare the Outback to the XC70, except the AWD. My daughter has a 2008 Outback, the seats are not comfortable, it is noisy, and the newer ones are very tall. Mpg for the Outback is pretty good if you don't cruise fast, but throttle response for a loaded car is pathetic. Not sure about what happens after 100K miles, but the headgaskets do fall apart with age. The timing belt/water pump change is a royal pain.
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My name is Klaus and I am a V♂lv♂holic